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


int main() {

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