#include <stdio.h>

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