#include <stdio.h>
#include <memory.h>
#include <algorithm>
#include <vector>
#include <iostream>
#include <string>
#include <set>
#include <map>
#include <bitset>
#include <queue>

using ii = std::pair<int, int>;

int main()
{
	int m, p, d, s;
	scanf("%d %d %d %d", &p, &d, &m, &s);

	int count = 0;
	while (true)
	{
		if (s < p)
			break;

		s -= p;
		count++;
		p = std::max(p - d, m);
	}

	printf("%d", count);

	return 0;
}