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


int main() {
     int p; 
    int d; 
    int m; 
    int s; 
cin>>p>>d>>m>>s;
   int i=0,val=p;
    while(s>0)
    {  s=s-p;
     i++;
        p=p-d;
        if(p<=m)
            p=m;
       
     
    }
    if(s==0)
        cout<<i;
    else
    cout<<i-1;
    return 0;
}