#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 */   
    long long p,d,m,s,cnt=0;
    cin>>p>>d>>m>>s;
    if (p<m) p=m;
    while (p<=s){
        s-=p;
        cnt++;
        p-=d;
        if (p<=m)p=m;
    }
    cout<<cnt<<"\n";
    return 0;
}