#include <iostream>
using namespace std;

int main() {
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	int arr[n][m];
	int num = 0;
	for(int i = 0; i < n; ++i) {
		int dir, j;
		if(i % 2 == 0){
			j = 0;
			dir = 1;
		}
		else {
			j = m-1;
			dir = -1;
		}
		for(; j < m&&j >= 0; j+= dir) {
			arr[i][j] = num;
			++num;
		}
	}
	cout << arr[x - 1][y - 1];
	return 0;
}