#include<bits/stdc++.h>
using namespace std; 
int p[100][100]={0},m,n,a,b;
long long ans=0;
void dp(int x,int y){
	if(p[x+1][y]==2){ans++;return;}
    if(p[x][y+1]==2){ans++;return;}
    if(p[x+1][y]==0&&x+1<=a)dp(x+1,y);
    if(p[x][y+1]==0&&y+1<=b)dp(x,y+1);
    return;
}
int main(){
scanf("%d%d%d%d",&a,&b,&m,&n);
p[a][b]=2;p[m][n]=1;p[m+2][n+1]=1;p[m+1][n+2]=1;
if(m>=1)p[m-1][n+2]=1;
if(m>=2)p[m-2][n+1]=1;
if(n>=1)p[m+2][n-1]=1;
if(n>=2)p[m+1][n-2]=1;
if(m>=2&&n>=1)p[m-2][n-1]=1;
if(m>=1&&n>=2)p[m-1][n-2]=1;
dp(0,0);
printf("%lld",ans);
return 0;
}