#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int  main()
{
    //fropen("in","r",stdin);
   // fropen("out","w",stdin);
    int n,m,a,b;

    while(scanf("%d%d%d%d",&n,&m,&a,&b)!=EOF)
    {
        int d,f,h;
        int v1,v2,v3,v4,k,l;
        v1=n/2+n%2;
        f=m/2+m%2;
        h=min(v1,f);
        d=max(v1,f);
        if(n==m&&n%2==1&&m%2==1&&h==min(a,b)&&d==max(a,b))
        {
            printf("%d\n",h-1);
            continue;
        }
        if(h==v1)
        {
            k=max(a-1,n-a);

            v2=min(k,min(m-b+1,b));
        }
        else
        {
            k=max(b-1,m-b);

            v2=min(k,min(n-a+1,a));
        }
        v2=max(v2,h);
        printf("%d\n",v2);
    }
    return 0;
}