#include <stdio.h>

int main(void){
	int a;
	long b,n,x,ans=0,mans=0;
	scanf("%ld", &a);
	scanf("%ld", &b);
	scanf("%ld", &n);
	for(x = 0; x <= n; x++){
		ans = (long)((a * x) / b) - (a * (long)(x / b));
		if(mans < ans)
			mans = ans;
	}
	printf("%ld", mans);
	return 0;
}