#include <iostream>
using namespace std;
#include <cstdio>
#include <string.h>
#include <stdlib.h>
#include <math.h>

#define FOR(i,a,b) for(int (i)=(a);i<(b);i++)

typedef long long ll;
typedef unsigned long long ull;
typedef long double lb;

/* ここからが本編 */


int main(void)
{
   int i,j,k,l;
   int x,y;
   int x2,y2;
   int ans;

   cin >> x >> y;

   cin >> x2 >> y2;

   if(x * x2 < 0) {
      x2 = 0; y2 = 0;
   }

   else if( y * y2 < 0) {
      x2 = 0; y2 = 0;
   }

   x = abs(x);
   y = abs(y);

   if(x > y) ans = x;
   else if(x < y) ans = y;
   /* こっからはx == yの条件が自然につく */
   else if(x > 2) ans = x;
   else if(x == 1) ans = 1;
   else if(x == 2) {
      if(x2 == 1 && y2 == 1) ans = 4;
      else ans = 2;
   }

   printf("%d\n",ans);
   return 0;
}