#include <stdio.h>
#include <math.h>
typedef unsigned short int uints_t;
typedef unsigned int uint_t;

int main(void){
	uints_t a;
	uint_t b, n;
	scanf("%hd %hd %hd", &a, &b, &n);
	int temp = 0;
	for(int i = 1; i <= n; i++){
		if(temp < floor(a*i/b)-a*floor(i/b))
		  temp = floor(a*i/b)-a*floor(i/b);
	}
	printf("%hd\n", temp);
	return 0;
}