救救孩子！笔芯

#include <bits/stdc++.h>
using namespace std;
#define ll long long
int n;
ll a1,b1,a2,b2,gc,x,y;
inline ll gcd(ll a,ll b)
{
	if(a%b==0)
		return b;
	return gcd(b,a%b);
}
inline void swap(ll &a,ll &b)
{
	ll c=a;
	a=b;
	b=c;
	return;
}
inline void exgcd(ll a,ll b)
{
	if(b==0)
	{
		x=1;
		y=0;
		return;
	}
	exgcd(b,a%b);
	ll c=x;
	x=y;
	y=c-a/b*y;
	return;
}
int main()
{
	std::ios::sync_with_stdio(0);
	cin>>n>>a1>>b1;
	for(int i=2;i<=n;i++)
	{
		cin>>a2>>b2;
//		if(b2<b1)
//			swap(a1,a2),swap(b1,b2);
		gc=gcd(a1,a2);
		exgcd(a1/gc,a2/gc);
		b1+=(b2-b1)/gc*x*a1;
		a1=a1/gc*a2;
		b1=(b1%a1+a1)%a1;
	}
	cout<<b1;
	return 0;
}