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

int main(){
	long long max, A, B, N, x;
	int i;

	scanf("%lld %lld %lld", &A, &B, &N);

	x = fmin(B-1, N);
	max = A*x/B - A*(x/B);

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