#include <bits/stdc++.h>
#define ll long long int
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 
    ll p,m,d,s;
    cin>>p>>d>>m>>s;
    ll n= ((p-m)/d)+1;
    ll x= n*(2*p-(n-1)*d)/2;
    //cout<<x<<" "<<n<<endl;
    if(x<=s) cout<<((s-x)/m)+n;
    else{
        ll ans=0;
        x=0;
        while(s>=x){
            x+=p;
            p-=d;
            ans++;
        }
        cout<<ans-1;
    }
    return 0;
}