#include<bits/stdc++.h>

 #define pa pair<int,int>

 #define CLR(a,x) memset(a,x,sizeof(a))

 using namespace std;

 typedef long long ll;

 const int maxn=,maxm=*,inf=1e9;

 inline ll rd(){

     ll x=;char c=getchar();int neg=;

     while(c<''||c>''){if(c=='-') neg=-;c=getchar();}

     while(c>=''&&c<='') x=x*+c-'',c=getchar();

     return x*neg;

 }

 struct Edge{

     int b,l,ne;

 }eg[maxm];

 int egh[maxn],ect=;

 int S,T,N,M;

 int cur[maxn],dep[maxn];

 queue<int> q;

 inline void adeg(int a,int b,int c){

     eg[++ect].b=b,eg[ect].l=c,eg[ect].ne=egh[a];egh[a]=ect;

     eg[++ect].b=a,eg[ect].l=,eg[ect].ne=egh[b];egh[b]=ect;

 }

 inline bool bfs(){

     CLR(dep,);CLR(cur,-);

     dep[S]=,q.push(S);

     while(!q.empty()){

         int p=q.front();q.pop();

         for(int i=egh[p];i;i=eg[i].ne){

             int b=eg[i].b;

             if(dep[b]||!eg[i].l) continue;

             dep[b]=dep[p]+,q.push(b);

         }

     }

     return dep[T];

 }

 int dinic(int x,int y){

     if(x==T) return y;

     int tmp=y;

     if(cur[x]==-) cur[x]=egh[x];

     for(int &i=cur[x];i;i=eg[i].ne){

         int b=eg[i].b;

         if(dep[b]!=dep[x]+||!eg[i].l) continue;

         int re=dinic(b,min(eg[i].l,tmp));

         tmp-=re,eg[i].l-=re,eg[i^].l-=re;

         if(!tmp) break;

     }return y-tmp;

 }

 int main(){

     //freopen("","r",stdin);

     int i,j,k;

     N=rd(),M=rd(),S=rd()+N,T=rd();

     for(i=;i<=N;i++)

         adeg(i,i+N,);

     for(i=;i<=M;i++){

         int a=rd(),b=rd();

         adeg(a+N,b,inf),adeg(b+N,a,inf);

     }

     int ans=;

     while(bfs()) ans+=dinic(S,inf);

     printf("%d\n",ans);

     return ;

 }