#define II int
#define IL inline
#define R register
#define I 123546
using namespace std;

template < typename T > IL void  (R T &a) {
    R char c=getchar (); R T w=1, p=0;
    while (!isdigit(c)) { if(c=='-') w=-1; c=getchar (); }
    while (isdigit(c)) { p=p*10+c-'0'; c=getchar (); }
    a=w*p;
}



II tot=1,n,m,s,t,ans,Inf=1e8;
II head[I], inq[I], bit[I];
queue <II> Q;

struct UUI { II to,up,flow; } aa[I];
IL void join(R II x,R II y,R II z) {
    aa[++tot]=(UUI) {y,head[x],z}; head[x]=tot;
    aa[++tot]=(UUI) {x,head[y],0}; head[y]=tot;
}

IL bool bfs() {
    for(R II i=1;i<=n<<1;i++) inq[i]=0;
    Q.push(s); inq[s]=1;
    while (!Q.empty()) {
        R II x=Q.front(); Q.pop();
        for(R II i=head[x],go;i;i=aa[i].up)
        {
            go=aa[i].to;
            if(!inq[go] && aa[i].flow) {
                inq[go]=inq[x]+1;
                Q.push(go);
            }
        }
    }
    return inq[t];
}

IL II dfs(R II x,R II a) {
    if(x==t || !a) return a;
    R II now_f=0,f;
    for(R II &i=bit[x],go;i;i=aa[i].up)
    {
        go=aa[i].to;
        if(inq[go]==inq[x]+1 && (f=dfs(go,min(aa[i].flow,a)))>0) {
            aa[i].flow-=f;
            aa[i^1].flow+=f;
            a-=f; now_f+=f;
            if(!a) return now_f;
        }
    }
    return now_f;
}

int main()
{
    //freopen("1.in","r",stdin);

    of(n); of(m); of(s); of(t); s+=n;
    for(R II i=1;i<=n;i++) join(i,i+n,1);
    for(R II i=1,x,y;i<=m;i++) {
        of(x); of(y);
        join(x+n,y,Inf);
        join(y+n,x,Inf);
    }
    
    while (bfs()) {
        for(R II i=1;i<=n<<1;i++) bit[i]=head[i];
        ans+=dfs(s,Inf);
    }
    
    printf("%dn",ans);
    exit(0);
}