#include<stdio.h>
#include <math.h>

int main(){
	long max = 0, temp, A, B, N, x;
	int i;
	//long max = 0, temp;
	scanf("%ld %ld %ld", &A, &B, &N);

	if(B<N) N = B;
	for(i=1; i<=N; i++){
		//printf("%d\n",i);
		temp = (A*i)/B - A*(i/B);
		//printf("%ld\n",temp);
		if(max < temp) max = temp;
	}

	printf("%ld", max);
	return 0;
}
