#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

using namespace std;

#define maxn 205

#define maxm 20005

#define INF 0x3f3f3f3f

int head[maxn],cnt=,n,m,E[maxm],V[maxm],F[maxm],s,t;

int que[maxm<<],deep[maxn],c1,c2;

inline void in(int &now)

{

    char Cget=getchar();now=;

    while(Cget>''||Cget<'') Cget=getchar();

    while(Cget>=''&&Cget<='')

    {

        now=now*+Cget-'';

        Cget=getchar();

    }

}

inline void edge_add(int u,int v,int f)

{

    E[++cnt]=head[u],V[cnt]=v,F[cnt]=f,head[u]=cnt;

    E[++cnt]=head[v],V[cnt]=u,F[cnt]=,head[v]=cnt;

}

bool bfs()

{

    memset(deep,-,sizeof(deep));

    int h=,tail=,now;que[]=s,deep[s]=;

    while(h<tail)

    {

        now=que[h++];

        for(int i=head[now];i;i=E[i])

        {

            if(deep[V[i]]<&&F[i])

            {

                deep[V[i]]=deep[now]+;

                if(V[i]==t) return true;

                que[tail++]=V[i];

            }

        }

    }

    return false;

}

int flowing(int now,int flow)

{

    if(t==now||flow<=) return flow;

    int oldflow=,pos;

    for(int i=head[now];i;i=E[i])

    {

        if(!F[i]||deep[V[i]]!=deep[now]+) continue;

        pos=flowing(V[i],min(flow,F[i]));

        flow-=pos,oldflow+=pos,F[i]-=pos,F[i^]+=pos;

        if(!flow) return oldflow;

    }

    if(!oldflow) deep[now]=-;

    return oldflow;

}

int main()

{

    in(n),in(m),in(c1),in(c2),s=c1+n,t=c2;

    for(int i=;i<=n;i++) edge_add(i,i+n,);

    while(m--)

    {

        in(c1),in(c2);

        edge_add(c1+n,c2,INF);

        edge_add(c2+n,c1,INF);

    }

    int ans=;

    while(bfs()) ans+=flowing(s,INF);

    cout<<ans;

    return ;

}