#include <algorithm>
#include <string.h>
#include <iostream>
#include <stdio.h>
#include <math.h>

using namespace std;

typedef long long ll;
typedef double db;
db a, b, n;
db x, x2 = -1;

int main() {
	cin >> a >> b >> n;
	
	x = floor(a * n / b) - a * floor(n / b);
	if (n > b) {
		db t = n / b * b - 1;
		x2 = floor(a * t / b) - a * floor(t / b);
	}

	cout << max(x, x2) << endl;
	
	return 0;
}