救命，为什么90分

#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
	long long a , b , n;
	cin >> a >> b >> n;
	long long m = n - 1;
	long long p = (long long)floor(a * m / b) - (long long)a * floor(m / b);
	long long q = (long long)floor(a * n / b) - (long long)a * floor(n / b);
    if(max(p , q) >= 0) cout << max(q , p);
    else cout << 0;
	return 0;
}