hihocoder1744 hohahola

思路：

二分。

实现：

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 0x3f3f3f3f;
ll n, x, y, z;
bool check(ll m)
{
    ll tmp = m * x - n * z;
    if (tmp <= 0) return true;
    else if (y > z && tmp <= m * (y - z)) return true;
    return false;
}
int main()
{
    while (cin >> n >> x >> y >> z)
    {
        ll l = 0, r = INF, ans = -1;
        while (l <= r)
        {
            ll m = l + r >> 1;
            if (check(m))
            {
                ans = m; l = m + 1;
            }
            else r = m - 1;
        }
        cout << ans << endl;
    }
    return 0;
}