#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;

int main() {
	int N, M, P, Q;
	cin >> N >> M >> P >> Q;

	int i = 1, cnt = 0;
	while (1) {
		if (N <= 0) {
			break;
		}
		else {
			if (i >= P && i <= (P + Q - 1)) {
				N -= (2 * M);
			}
			else {
				N -= M;
			}
			cnt++;
		}

		if (i >= 1 && i <= 11) {
			i++;
		}
		else {
			i = 1;
		}
	}

	cout << cnt << endl;
}