#include <stdio.h>
typedef long long ll;
ll max(ll x, ll y) {
	return x > y ? x : y;
}
int main() {
	ll a, b, n;
	scanf("%lld%lld%lldd", &a, &b, &n);
	ll x = n / b * b - 1;
	printf("%lld\n", max(a * x / b - a * (x / b), a * n / b - a * (n / b)));
	return 0;
}
