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


int main() {
    int p,d,m,s;
    cin>>p>>d>>m>>s;
    int cnt = 0;
    while(s>0) {
        s -= p;
        if(s<0) {
            break;
        }
        p -= d;
        if(p<=m) {
            p = m;
        }
        cnt++;
    }
    cout<<cnt<<endl;
    return 0;
}