#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    int count = -1;
    vector<int> costs;
    costs.push_back(p);
    int init = p - d;
    while(init >= m){
        costs.push_back(init);
        init = init - d;
    }
    int money = s;
    int flag = 0;
    for(int i = 0 ; i < costs.size() ; i++) {
        if( money >= 0 ) {
            money = money - costs[i];
            count++;
        }
        else{
            flag = 1;
            break;
        }
    }
    if(flag == 1)
        return count;
    
    while(money >= 0) {
        money = money - m;
        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;
}