#include <bits/stdc++.h>
#define pb push_back
#define long long long
#define pll pair < long , long >
#define vll vector < pll >
#define ml map < long , long >
#define mll map < pll , long >
#define x first
#define y second
#define vl vector < long >
#define io ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
using namespace std;

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