#include <stdio.h>
#include <math.h>

int main()
{
	long long int Point;
	long long int PointMax = 0;
	long long int X = 1;
	long long int A, B, N;

	scanf("%lld%lld%lld", &A, &B, &N);

	while (X <= N) {
		Point = floor(A*X / B) - A * floor(X / B);
		if (Point > PointMax) {
			PointMax = Point;
		}
		X++;
	}

	printf("%lld\n", PointMax);

	return 0;
}