#include <stdio.h>

int main()
{
	long long A, B, N;
	scanf("%lld %lld %lld", &A, &B, &N);
	if (N / B >= 1) N = N / B * B - 1;
	printf("%lld\n", A * N / B - A * (N / B));	
	fflush(stdout);
	return 0;
}