#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) temp = (A*(B-1))/B - A*((B-1)/B);
	else temp = (A*N)/B - A*(N/B);

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