#include<stdio.h>

int main(void){

	long long int A, B, N;
	long long int x, c;
	long long int ans = 0;


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

	for(x = 0; x <= N; x++){
		c = (A * x) / B - A *( x / B);
		if(ans < c)
			ans = c;
	}

	printf("%d", ans);

	return 0;
}