#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 */  
    int p,d,m,s;
    int sum=0;
    int count=0;
    cin>>p>>d>>m>>s;
    while(sum<=s)
    {
        sum=sum+p;
        count++;
      
            p=p-d;
       
        if(p<m)
        {
            p=m;
        }
    }
    cout<<count-1;
    return 0;
}