#include <iostream>
#include <algorithm>
#include <time.h>
#include <stack>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <cassert>

using namespace std;

const int N = 100005;
const int inf = 1000 * 1000 * 1000;
const int mod = 1000 * 1000 * 1000 + 7;

int p,d,m,s;

int main(){
    cin>>p>>d>>m>>s;
    int answ = 0 , k = 0;
    while(answ + p <= s){
        answ += p;
        k++;
        p -= d;
        p = max(p , m);
    }
    cout<<k<<endl;
    return 0;
}