#include<bits/stdc++.h>
using namespace std;

int bn, bm, cn, cm;

int dfs(int n, int m) {
    if(n == 0 && m == 0) return 1;
    if(n < 0 || m < 0) return 0;
    if(n == cn && m == cm || (n == cn-2 && (m == cm-1 || m == cm+1)) || (n == cn-1 && (m == cm-2 || m == cm+2)) || (n == cn+1 && (m == cm-2 || m == cm+2)) || (n == cn+2 && (m == cm-1 || m == cm+1))) return 0;
    return dfs(n-1, m) + dfs(n, m-1);
}

int main() {
	cin >> bn >> bm >> cn >> cm;
	cout << dfs(bn, bm);
	return 0;
}