#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
typedef long long int ll;
using namespace std;


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