#include <bits/stdc++.h>
#define ALL(a) (a).begin(), (a).end()
#define SZ(a) ((int)(a).size())
#define FIN ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define pb push_back
#define fore(i,a,b) for(int i = a; i < b; i++)
using namespace std;
typedef long long ll;

int M, P, S, D;

int main(){
        cin >> P >> D >> M >> S;
        int price=P,ans=0;
        while(S >= price){
                S -= price;
                price = max(price-D, M);
                ans++;
        }
        cout << ans << "\n";
}