#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;const int INF=0x7FFFFFFF;
const int maxn=200*200+10;
const int Maxn=200+10;
int N,M;
int U[maxn],V[maxn];
int F[Maxn];
vector<int>G[Maxn];
int St;
int dis[Maxn],flag[Maxn];
queue<int>Q;
int Belong[Maxn];int nx,ny;
int g[Maxn][Maxn];
int cx[Maxn],cy[Maxn];
int mk[Maxn];void init()
{for(int i=0; i<=N; i++) G[i].clear();memset(F,0,sizeof F);memset(Belong,0,sizeof Belong);for(int i=0; i<=N; i++) dis[i]=INF;nx=N,ny=N;memset(g,0,sizeof(g));
}void SPFA()
{while(!Q.empty()) Q.pop();memset(flag,0,sizeof flag);flag[St]=1;dis[St]=0;Q.push(St);while(!Q.empty()){int h=Q.front();Q.pop();flag[h]=0;for(int i=0; i<G[h].size(); i++){if(dis[h]+1<dis[G[h][i]]){dis[G[h][i]]=dis[h]+1;if(!flag[G[h][i]]){flag[G[h][i]]=1;Q.push(G[h][i]);}}}}
}int path(int u)
{for(int v=1; v<=ny; v++){if(g[u][v]&&!mk[v]){mk[v]=1;if(cy[v]==-1||path(cy[v])){cx[u]=v;cy[v]=u;return 1;}}}return 0;
}int MaxMatch()
{int res=0;memset(cx,-1,sizeof(cx));memset(cy,-1,sizeof(cy));for(int i=1; i<=nx; i++){if(cx[i]==-1){memset(mk,0,sizeof(mk));res=res+path(i);}}return res;
}int main()
{while(~scanf("%d%d",&N,&M)){init();for(int i=1; i<=M; i++) scanf("%d%d",&U[i],&V[i]);for(int i=1; i<=M; i++){G[U[i]].push_back(V[i]);G[V[i]].push_back(U[i]);}for(int i=1; i<=N; i++)if(dis[i]==INF) St=i,SPFA();for(int i=1; i<=N; i++){if(dis[i]%2==0) Belong[i]=2;else Belong[i]=1;}int Fail=0;for(int i=1; i<=M; i++)if(Belong[U[i]]==Belong[V[i]]){Fail=1;break;}if(Fail==1) printf("No\n");else{for(int i=1; i<=M; i++){if(Belong[U[i]]==1&&Belong[V[i]]==2)g[U[i]][V[i]]=1;if(Belong[V[i]]==1&&Belong[U[i]]==2)g[V[i]][U[i]]=1;}printf("%d\n",MaxMatch());}}return 0;
}