#include <iostream>
 #include <stdio.h>
 #include <string.h>
 #include <algorithm>
 using namespace std;
 int n,m,x,y,s,l;
 int main()
 {
     while(~scanf("%d%d%d%d",&n,&m,&x,&y)){
         if(m > n){
             s = max(n-x,x-);
             s = min(s,min(m-y+,y));
         }
         else{
             s = max(m-y,y-);
             s = min(s,min(n-x+,x));
         }
             l = min((m+)/,(n+)/);
             s = max(s,l);
          ==  && x == y && x == (n+)/)
             s -= ;
         printf("%d\n",s);
     }
     ;
 }