#include <bits/stdc++.h>
using namespace std;

/*void main()
{
    int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    
    int i ;
    int counter = 0 , store =  0 , a = 0 ;
     a =  p ;
    for(i=0;i<10000;i++)
    {
        a = a - p * i;
        
        if(6 >= a)
        {
            store = store +  6;
        }
        else
        {
            store = store + a;
        }
        if(store<=s)
            counter++;
    }
    cout<<counter;
}
*/
int main() {
    /*int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    int answer = howManyGames(p, d, m, s);
    //cout << answer << endl;*/
    //int cn ;
      int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    
    int i ;
    int counter = 0 , store =  0 , a = 0 ;
     a =  p ;
   while(store<m)
   {
       a=a-d;
       store  =  store +  a;
       if(store<=s)
           counter ++ ;
   }
    
    if(store<=s)
    {
        while(store<=s)
        { store = store + m;
        counter++;
        }
    }
    
    cout<<counter/2;
    return 0;
}