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


int main() {
    long int p,d,m,s,x=0;
    cin>>p>>d>>m>>s;
    while(s>=p){
        x++;
        s-=p;
        p=max(p-d,m);
    }
    cout<<x<<endl;
    return 0;
}