#include<stdio.h>

int main(){
	long int A, B, N;
	scanf("%ld %ld %ld", &A, &B, &N);
	if(N > B){
		printf("%ld", (long int) (A * ((B - 1) / (double) B)));
	}
	else{
		printf("%ld", (long int) (A * (N / (double) B)));
	}

	return 0;
}