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


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