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

typedef long long int64;
typedef unsigned long long uint64;

#define min(a,b) (((a) < (b)) ? (a) : (b))

int main()
{

	uint64 a, b, n;

	scanf("%llu %llu %llu", &a, &b, &n);

	printf("%llu", (uint64)floor(a * min(b - 1, n) / b));

	return 0;
}
