#include <bits/stdc++.h>
#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 int p,d,m,s;
    long long int n=0,sum=0;
    cin>>p>>d>>m>>s;
    while(sum<=s)
    {
        sum+=p;
        p-=d;
        if(p<m)
            p=m;
        if(sum<=s)
            n++;
    }
    cout<<n<<endl;
    return 0;
}