#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
using namespace std;
typedef long long ll;
inline int read()
{int x=0,f=1; char ch=getchar();while(ch<'0'||ch>'9') { if(ch=='-') f=-1; ch=getchar(); }while(ch>='0'&&ch<='9') { x=(x<<1)+(x<<3)+(ch^48); ch=getchar(); }return x*f;
}
const int N=1e5+7,M=4e6+7,INF=1e9+7;
int fir[N],from[M],to[M],val[M],cntt=1;
inline void add(int a,int b,int c)
{from[++cntt]=fir[a]; fir[a]=cntt;to[cntt]=b; val[cntt]=c;from[++cntt]=fir[b]; fir[b]=cntt;to[cntt]=a; val[cntt]=0;
}
int dep[N],Fir[N],S,T;
queue <int> q;
bool BFS()
{for(int i=S;i<=T;i++) Fir[i]=fir[i],dep[i]=0;q.push(S); dep[S]=1; int x;while(!q.empty()){x=q.front(); q.pop();for(int i=fir[x];i;i=from[i]){int &v=to[i]; if(dep[v]||!val[i]) continue;dep[v]=dep[x]+1; q.push(v);}}return dep[T]>0;
}
int DFS(int x,int mxf)
{if(x==T||!mxf) return mxf;int fl=0,res;for(int &i=Fir[x];i;i=from[i]){int &v=to[i]; if(dep[v]!=dep[x]+1||!val[i]) continue;if( res=DFS(v,min(mxf,val[i])) ){mxf-=res; fl+=res;val[i]-=res; val[i^1]+=res;if(!mxf) break;}}return fl;
}
inline int Dinic() { int res=0; while(BFS()) res+=DFS(S,INF); return res; }int n,m;
char s[N];
int main()
{n=read(),m=read();scanf("%s",s+1);S=0,T=n*4+1; int a,b;for(int i=1;i<=n;i++){if(s[i]=='J') add(S,i,1),add(i,n+i,1);if(s[i]=='T') add(n*3+i,T,1);else add(n+i,n*2+i,1);}for(int i=1;i<=m;i++){a=read(),b=read();if(s[a]!='T'&&s[b]!='T') add(a,n+b,1),add(b,n+a,1);if(s[a]!='T'&&s[b]=='T') add(n*2+a,n*3+b,1);if(s[b]!='T'&&s[a]=='T') add(n*2+b,n*3+a,1);}printf("%d",Dinic());return 0;
}