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