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 <= ) return true;
     else if (y > z && tmp <= m * (y - z)) return true;
     return false;
 }
 int main()
 {
     while (cin >> n >> x >> y >> z)
     {
         ll l = , r = INF, ans = -;
         while (l <= r)
         {
             ll m = l + r >> ;
             if (check(m))
             {
                 ans = m; l = m + ;
             }
             else r = m - ;
         }
         cout << ans << endl;
     }
     return ;
 }