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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    long long p, d, m, s;
    cin >> p >> d >> m >> s;
    long long count = 0;
    long long sum = p;
    while(sum <= s) {
        count += 1;
        if( p-d <= m) p = m;
        else p -= d;
        sum += p;
    }
    cout << count << endl;
    return 0;
}