#include <stdio.h>

int main()
{
	long long int n,x,a,b,value,v1;
	
	scanf("%lld %lld %lld",&a,&b,&n);
	
	value = 0;
	
	for(x = 1;x <= n;x++)
	{
		v1 = (a * x / b) - a * (x / b);
		if(v1 > value)
			value = v1;
	}
	
	printf("%lld\n",value);
	
	return 0;
}