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

int main()
{
	ll A,B,N;
	scanf("%lld %lld %lld", &A,&B,&N);
	ll i = N;
	ll x;
	ll max = LLONG_MIN;
	ll sum = 0;
	while (i >= N - 2)
	{
		sum = (A*i/B) - A * (i/B);
		if (sum >= max)
		{
			x = i;
			max = sum;
		}
		i--;
	}
	printf("%lld\n",max);
	return (0);
}
