表达整数的奇怪方式

题目:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll exgcd(ll a,ll b,ll &x,ll &y)
{
    if(b==0)
    {
        x=1;
        y=0;
        return a;
    }
    ll gcd;
    gcd=exgcd(b,a%b,y,x);
    y-=a/b*x;
    return gcd;
}
int main()
{
    ll n;
    cin>>n;
    ll a1,m1;
    cin>>a1>>m1;
    for(int i=1;i<n;i++)
    {
        ll a2,m2;
        cin>>a2>>m2;
        ll k1,k2;
        ll d=exgcd(a1,a2,k1,k2);
        if((m2-m1)%d)
        {
            cout<<"-1"<<endl;
            return 0;
        }
        k1*=(m2-m1)/d;
        ll t=abs(a2/d);
        k1=(k1%t+t)%t;
        m1=a1*k1+m1;
        a1=abs(a1*a2/d);
    }
    cout<<(m1%a1+a1)%a1<<endl;
    return 0;
}