#include <bits/stdc++.h>

using namespace std;
using namespace std::chrono;

#define rep(i,a,b) for(int i = a;i<(b);++i)
#define trav(a,v) for(auto& a : v)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef vector<int> vi;

ll big = 1000000007ll;
ll big2 = 1000000009ll;
ll n,m,k,q,w,h,x,y;


int main()
{
   // freopen("input.txt","r",stdin);
    //freopen("autput.txt","w",stdout);
    ll a,b,c,d,e;
    ll s,p;
    cin >> p >> d >> m >> s;

    ll ans = 0;
    while(s >= p){
        ans++;
        s -= p;
        p -= d;
        p = max(p,m);
    }
    cout << ans << "\n";

    return 0;
}