// Starting with the name of Allah

#include<stdio.h>
int main()
{
	long long int a,b,c;
	scanf("%lld %lld %lld",&a,&b,&c);
	if(c>=b-1){
		printf("%lld\n",(a*(b-1))/b);
	}
	else{
		printf("%lld\n",(a*c)/b);
	}
	return 0;
}
