#include <iostream>
#include <string>
using namespace std;
int main() {
	int N, M, P, Q;
	cin >> N >> M >> P >> Q;
	int month = 0;
	int i = 1;
	while (true) {
		if (i >= P && i <= P + (Q - 1)) {
			N -= M*2;
			month++;
		}
		else {
			N -= M;
			month++;
		}
		i++;
		if(i == 13)i = 1;
		if(N <= 0)break;
	}
	cout << month << endl;
	return 0;
}