#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    int sum = 0 ;
    //int flag = 0 ;
    int count = 0 ;
    if(s >= p )
    {
        sum = p ;
        count++;
        if(s == sum )
        {
            return 1;
        }
    }
    else if(s < p)
    {
       return 0;
    }
    int temp = p;
    while(sum <= s)
    {
        
        if(temp > m )
        {
            temp = temp - d ;
            if(temp < m )
            {
                temp = m ;
                //flag = 1 ;
            }
        }
        sum += temp ;
        count++;
    }
    count--;
    return  count;
}

int main() {
    int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    int answer = howManyGames(p, d, m, s);
    cout << answer << endl;
    return 0;
}