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

int main(){
int p,d,m,s;
cin>>p>>d>>m>>s;
int i,j;
int x=(p-m)/d+1;
if(x<=0){


    int y=s/m;
    cout<<y<<endl;
    return 0;


}
else{

    int u=x*(2*p-d*(x-1))/2;
    if(u<=s){
        int ans=x;
        ans=ans+(s-u)/m;
        cout<<ans<<endl;



    }
    else{
        int ans=0;
       for(i=1;i<=x;i++){

        int u=i*(2*p-d*(i-1))/2;
        if(u<=s){
            ans=i;
        }
        else break;

       }



        cout<<ans<<endl;


    }



}











return 0;}