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


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