#include <bits/stdc++.h>

using namespace std;
int main() {
    int a,b,c,d,s=0,x=0;cin>>a>>b>>c>>d;
    while(s<d)
    {
        s+=a;if(a>c) a-=b; if(a<c){a=c;}
        if(s>d) break; x++;
    }
    cout<<x;
    return 0;
}