/*POJ  2723 Get Luffy OutAC代码 */

#include<stdio.h>#include<math.h>#include<iostream>using namespace std;const int MAXN=1<<12;const int MAXM=1<<24;struct Node{int l,r;}e[MAXN];struct Node1{int from,to,next;}edge1[MAXM],edge2[MAXM];int visit1[MAXN],visit2[MAXN],head1[MAXN],head2[MAXN],Belong[MAXN],T[MAXN];int tol1,tol2,Bcnt,Tcnt;int hash[MAXN];void add(int a,int b){    edge1[tol1].from=a;edge1[tol1].to=b;edge1[tol1].next=head1[a];head1[a]=tol1++;    edge2[tol2].from=b;edge2[tol2].to=a;edge2[tol2].next=head2[b];head2[b]=tol2++;} void dfs1(int x){int j;    visit1[x]=1;for(j=head1[x];j!=-1;j=edge1[j].next)if(visit1[edge1[j].to]==0)  dfs1(edge1[j].to);    T[Tcnt++]=x;}           void dfs2(int x){int j;    visit2[x]=1;    Belong[x]=Bcnt;for(j=head2[x];j!=-1;j=edge2[j].next)if(visit2[edge2[j].to]==0)  dfs2(edge2[j].to);}       int main(){int i,j,n,m;int right,left,mid,ans;while(scanf("%d%d",&n,&m)!=EOF)    {

if(n==0&&m==0)break;int a,b;for(i=0;i<n;i++)        {            scanf("%d%d",&a,&b);            hash[a]=b;            hash[b]=a;        }       for(i=0;i<m;i++)           scanf("%d%d",&e[i].l,&e[i].r);        left=0;        right=m;while(left<=right)        {            mid=(left+right)/2;for(i=0;i<4*n;i++)            {                head1[i]=-1;                head2[i]=-1;                visit1[i]=0;                visit2[i]=0;            }              tol1=tol2=0;            Tcnt=Bcnt=0;for(i=0;i<2*n;i++)            {                add(i,hash[i]+2*n);            }    for(i=0;i<mid;i++)            {

if(e[i].l!=e[i].r)                {                    add(e[i].l+2*n,e[i].r);                    add(e[i].r+2*n,e[i].l);                }    if(e[i].l==e[i].r)                {                    add(e[i].l+2*n,e[i].l);                }        

            }for(i=0;i<4*n;i++)if(!visit1[i])  dfs1(i);      for(i=Tcnt-1;i>=0;i--)            {if(!visit2[T[i]])                {                    dfs2(T[i]);                    Bcnt++;                }                }    for(i=0;i<2*n;i++)            {if(Belong[i]==Belong[i+2*n]) break;            }    if(i>=2*n)            {                ans=mid;left=mid+1;            }    else  right=mid-1;        }            printf("%d\n",ans);    }    return 0;}   

/*POJ  2723 Get Luffy OutAC代码 */#include<stdio.h>#include<math.h>#include<iostream>using namespace std;const int MAXN=1<<12;const int MAXM=1<<24;int n,m;struct Node{int l,r;}e[MAXN];struct Node1{int from,to,next;}edge[MAXM];int ecnt;int head[MAXN],Belong[MAXN],Stack[MAXN];int top,idx,b_cnt;int hash[MAXN];int DFN[MAXN],LOW[MAXN];bool Instack[MAXN];void add(int a,int b){    edge[ecnt].from=a;edge[ecnt].to=b;edge[ecnt].next=head[a];head[a]=ecnt++;

} void Tarjan(int u){int i,v;    DFN[u]=LOW[u]=(++idx);    Stack[++top]=u;    Instack[u]=true;for(i=head[u];i!=-1;i=edge[i].next)    {        v=edge[i].to;if(!DFN[v])        {            Tarjan(v);if(LOW[u]>LOW[v])LOW[u]=LOW[v];        }    else if(Instack[v]&&LOW[u]>DFN[v])           LOW[u]=DFN[v];    }if(LOW[u]==DFN[u])    {        b_cnt++;do        {            v=Stack[top--];            Instack[v]=false;            Belong[v]=b_cnt;        }while(u!=v);       }        

}      int solve(){int i;    b_cnt=idx=top=0;for(i=0;i<4*n;i++)    {        DFN[i]=LOW[i]=0;        Belong[i]=0;        Instack[i]=false;    }    for(i=0;i<4*n;i++)if(!DFN[i])  Tarjan(i);for(i=0;i<2*n;i++)    {if(Belong[i]==Belong[i+2*n])return 0;    }    return 1;}        int main(){int i,j;int right,left,mid,ans;while(scanf("%d%d",&n,&m)!=EOF)    {

if(n==0&&m==0)break;int a,b;for(i=0;i<n;i++)        {            scanf("%d%d",&a,&b);            hash[a]=b;            hash[b]=a;        }       for(i=0;i<m;i++)           scanf("%d%d",&e[i].l,&e[i].r);        left=0;        right=m;while(left<=right)        {            mid=(left+right)/2;for(i=0;i<4*n;i++)            {                head[i]=-1;            }              ecnt=0;for(i=0;i<2*n;i++)            {                add(i,hash[i]+2*n);            }    for(i=0;i<mid;i++)            {

if(e[i].l!=e[i].r)                {                    add(e[i].l+2*n,e[i].r);                    add(e[i].r+2*n,e[i].l);                }    if(e[i].l==e[i].r)                {                    add(e[i].l+2*n,e[i].l);                }        

            }

if(solve())            {                ans=mid;left=mid+1;            }    else  right=mid-1;        }            printf("%d\n",ans);    }    return 0;}