#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int start, step, finish, have;
    int count = 0;
    cin >> start >> step >> finish >> have;
    int current = start;
    while (current <= have) {
        have -= current;
        count ++;
        current -=step;
        if (current < finish) {
            current = finish;
        }
    }
    cout << count;
    
    return 0;
}