#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 n;
	ll sum;
	if (N >= B - 1)
		x = B - 1;
	else if (N < B)
		x = N;
	sum = (A*x/B) - A * (x/B);
	printf("%lld\n", sum);
	return (0);
}
