PJU2891-Strange Way to Express Integers

#include<cstdio>
#include<iostream>
using namespace std;

typedef long long LL;

LL x,y;

LL Extended_Euclid(LL a,LL b)
{
	if (b==0)
	{
		y = 0;
		x = 1;
		return a;
	}
	LL d = Extended_Euclid(b,a%b);
	LL t = x;
	x = y;
	y = t-(a/b)*y;
	return d;
}

int main()
{
	int n;
	LL m1,m2,b1,b2;
	while (scanf("%d", &n) != EOF)
	{
		bool flag = false;
		scanf("%I64d%I64d", &m1, &b1);
		for (int i=1; i<n; i++)
		{
			scanf("%I64d%I64d", &m2, &b2);
			if (flag) continue;
			LL r = b2-b1;
			LL d = Extended_Euclid(m1,m2);
			if (r%d!=0)
			{
				flag = true;
				continue;
			}
			LL t = m2/d;
			x = ((r/d*x)%t+t)%t;
			b1 = m1*x+b1;
			m1 = m1*m2/d;
		}
		printf("%I64d\n", flag?-1:b1);
	}
	return 0;
}