#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    int tot=0;
    int sum=p,tempsum=p;
    if (p>s) return 0;
    while(sum<=s){
        if(tempsum>m) {tempsum-=d;
                 if(tempsum>m){ sum=sum+tempsum; tot++;}
                   }
        else {
            tempsum+=d;
            tempsum=m;
           // cout<<tempsum<<endl;
            sum+=tempsum;
            tot++;
        }
       } return tot;
}

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;
    return 0;
}