#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 */   
    int p,d,m,s;
    
    cin >> p >> d >> m >> s;
    
    int n = 0;
    
    int paid = 0;
    
    while(s >= paid + p) {
        ++n;
        paid += p;
        if (p > m) { p -= d; }
        if (p < m) p = m;
    }
        
    cout << n << endl;
        
    return 0;
}