nyoj 1235 A/B Problem

#include<string.h>
#include<stdio.h>
#define INF 0x3fffffff
long long x,y;
long long extend_gcd(long long a,long long b,long long &x,long long &y)
{    
	if(a==0&&b==0)return -1;
	if(b==0)
	{
        x=1;y=0;
        return a;
    }
    long long d=extend_gcd(b,a%b,y,x);
    y-=x*(a/b);
    return d;
}
int main()
{
	int T;
	scanf("%d",&T);
	while(T--)
	{
		int n,b;
		int m=9973;
		long long  b1;
		scanf("%d %d",&n,&b);
		long long gcd=extend_gcd(b,m,x,y);
		if(gcd==1)
			b1=(x%m+m)%m;
		else 
			b1=-1;	
		printf("%lld\n",(n*b1)%m);
	}	
	return 0;
}