#include <bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(),(x).end()
#define pb push_back
#define F first
#define S second
typedef vector<int> vi;
typedef long long ll;
typedef pair<int,int> ii;
template<class T,class U>void smin(T &a,U b) { if(a > b) a = b; }
template<class T,class U>void smax(T &a,U b) { if(a < b) a = b; }
const ll mod=1000000007;
const int N = 2e5+10;
const int M = 2e6;

int main()
{
//    freopen("input.txt","r",stdin);
    int p,d,m,s;
    cin>>p>>d>>m>>s;
    int cnt=0,cur = p;
    for(cnt = 0;;++cnt)
    {
        if(s >= cur)
        {
            s-=cur;
            cur = max(m,cur-d);
        }
        else break;
    }
    cout<<cnt;
}