#include <bits/stdc++.h>
using namespace std;

#define pb push_back

typedef pair<int, int> ii;
typedef long long ll;

int main()
{
    int p, d, m, s;
    scanf("%d%d%d%d", &p, &d, &m, &s);

    int cnt = 0;
    while (s > 0) {
        if (s-p < 0)
            break;
        ++cnt;
        s -= p;
        p -= d;
        if (p < m)
            p = m;
    }

    printf("%d", cnt);
    return 0;
}