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


int main() {
    long long p,d,m,s;
    cin>>p>>d>>m>>s;
    long long cost = p,cnt = 0;
    while(s>0){        
        if(cost<=s){
            ++cnt;
            s-=cost;
        }
        else
            break;
        cost = max(cost-d,m);
    }
    cout<<cnt;      
    return 0;
}