#include <bits/stdc++.h>
using namespace std;
int n,a,na,b,c,m,ma,num,i,x,y;
long long location[1000][1000];
long long TnT;
int im,jm,nm,mm;
int main(){
       y=1;
       while(y<=505){
                x=1;
                while(x<=y){
                        if(x==1||x==y) num=1;
                        else num=location[x-1][y-1]+location[x][y-1];
                location[x][y]=num;
                x++;
                }
        y++;
        }
        cin>>im>>jm>>nm>>mm;
        TnT=location[jm+1][im+1]+location[mm+1][nm+1];
        cout<<TnT;
        return 0;
}