#include<bits/stdc++.h>

using namespace std;

int p,d,m,s;

int cal()
{
    int sum=0;
    int c=p;
    while(s>=c)
    {
        s-=c;
        c-=d;
        if(c<m) c=m;
        sum++;
    }

    return sum;
}

int main()
{
    cin>>p>>d>>m>>s;


    cout<<cal()<<endl;
    return 0;
}