#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 cntr = 0;
    while(s-p>=0){
        cntr++;
        s -= p;
        p-=d;
        p = max(p,m);
    }
    cout<<cntr<<endl;
    return 0;
}