#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef long long ll;

int main()
{
	ll A,B,N;
	scanf("%lld %lld %lld", &A,&B,&N);
	ll i = N;
	ll sum;
	ll max = -99999999;
	while (i > 0)
	{
		sum = A*(i%B)/B ;
		if (max <= sum)
		{
			max = sum;
		}
		i--;
	}
	printf("%lld\n", max);
	return (0);
}