#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 */ 
    int p,d,s,m;
    cin >> p>>d>>m>>s;
    int i,cost=0,count=0;
    i=p;
    while(cost<=s)
    {
        count++;
        cost+=i;
        if((i-d)>=m)
            i-=d;
        else
            i=m;
    }
    cout<<count-1;
    return 0;
}