#include<bits/stdc++.h>
using namespace std;
int main () {
    int p,d,m,sum;
    cin>>p>>d>>m>>sum;
    int n=100000000;
    p=p+d;
    int ans=0,cur;
    for (int i=1;i<=n;i++){
        cur=max(m,p-d);
        ans+=cur;
        p-=d;
        if (ans>sum){
            cout<<i-1<<endl;
            return 0;
        }
    }
}