#include <bits/stdc++.h>
#define loop(i,k,n) for(int i=k;i<n;i++)
#define rloop(i,k,n) for(int i=k;i>=n;i--)
#define tests int t; cin>>t; cin.ignore(); while(t--)
#define input(a,n) for(int i=0;i<n;i++) cin>>a[i];
#define lli long long int
#define ld long double
#define pb push_back
using namespace std;


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