#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 c = 0;
    while(s >= p) {
        c++;
        s -= p;
        if(p>m) {
            p -= d;
        }
        if(p< m) {
            p = m;
        }
    }
    cout<<c;
    
    return 0;
}