#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,m,s,ans=0;
    cin>>p>>d>>m>>s;
    if(p<=s){
        s -= p;
        ans++;
        int n = (p-m)/d;
        int sum = n*(2*p-(n+1)*d)*0.5;
        if(sum <= s){
         ans += n;
            s -= sum;
            ans += s/m;
        }
        else{
           n = (d-2*p + sqrt((2*p-d)*(2*p-d)+8*s))*0.5;
           ans += n;
        }
    }
    cout<<ans;
    return 0;
}