#include <stdio.h>
int main(void){
	long a;
	long b;
	long n;
	scanf("%ld", &a);
	scanf("%ld", &b);
	scanf("%ld", &n);
	if(n/b < 1){
		printf("%ld\n", (a*n/b));
	}
	else{
		printf("%ld\n", (a*(b-1)/b));
	}
	return 0;
}