#include <iostream>
#include <cmath>
#define ll long long
using namespace std;

ll df[25][25];

ll fun(ll n, ll m, ll a, ll b) {
	if (df[n][m])
		return df[n][m];
	if (abs(n - a) == 2 && abs(m - b) == 1 || abs(n - a) == 1 && abs(m - b) == 2 || n == a && m == b) {
		return 0;
	} else if (m == 0 || n == 0) {
		df[n][m] = 1;
	} else {
		df[n][m] = fun(n - 1, m, a, b) + fun(n, m - 1, a, b);
	}
	return df[n][m];
}

int main() {
	ll n, m, a, b;
	cin >> n >> m >> a >> b;
	cout << fun(n, m, a, b) << endl;

	return 0;
}