#include <bits/stdc++.h>
using namespace std;

typedef vector<int> vi;
typedef pair<int, int> ii;
typedef long long ll;
typedef pair<long long, long long> l4;
typedef vector<long long> vll;
typedef double db;
typedef vector<double> vdb;
typedef pair<double, double> dd;
typedef set<int> si;
typedef set<long long> sll;
#define fi first
#define se second
#define matrix(a) vector< vector<a> >
#define sz(a) int((a).size()) 
#define lop(i,a,b) for (int i=a; i<=b; i++)
#define vlop(i,v) lop(i,0,sz(v)-1)
#define vlop1(i,v) lop(i,1,sz(v)-1)
#define rlop(i,a,b) for (int i=b; i>=a; i--)
#define vrlop(i,v) rlop(i,0,sz(v)-1)
#define vrlop1(i,v) rlop(i,1,sz(v)-1)
#define printv(i,v) vlop(i,v)cout<<v[i]<<" "
#define printv1(i,v) vlop1(i,v)cout<<v[i]<<" "
#define all(s) (s).begin(),(s).end()
#define pb push_back
#define enter cout<<'\n'
#define lb(i,v) int(lower_bound(all(v),i)-v.begin())
#define ub(i,v) int(upper_bound(all(v),i)-v.begin())


int main() {
    int p,d,m,s,c=0,count=0,pp;
    cin>>p>>d>>m>>s;
    pp=p;
    while(c<=s){
        count++;
        c+=pp;
        pp=max(pp-d,m);
    }
    cout<<count-1;
    return 0;
}