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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    long long int p, d, m, s, total_price, count;
    
    cin >> p >> d >> m >> s;
    
    total_price = 0;
    count = 0;
    while(total_price <= s){
        count++;
        total_price += p;
        int temp = p-d;
        if (temp>=m){
            p = temp;
        }
        else{
            p = m;
        }
    }
    
    cout << count-1;
    return 0;
}