bzoj Strange Way to Express Integers【excrt】

#include<iostream>
#include<cstdio>
using namespace std;
const long long N=100005;
long long n,r[N],m[N];
void exgcd(long long a,long long b,long long &d,long long &x,long long &y)
{
    if(b==0)
    {
        d=a,x=1,y=0;
        return;
    }
    exgcd(b,a%b,d,y,x);
    y-=a/b*x;
}
long long excrt()
{
    long long M=m[1],R=r[1],x,y,d;
    for(long long i=2;i<=n;i++)
    {
        exgcd(M,m[i],d,x,y);
        if((r[i]-R)%d)
            return -1;
        x=(r[i]-R)/d*x%(m[i]/d);
        R=R+x*M;
        M=M/d*m[i];
        R%=M;
    }
    return R>0?R:R+M;
}
int main()
{
    while(~scanf("%lld",&n))
    {
        for(long long i=1;i<=n;i++)
            scanf("%lld%lld",&m[i],&r[i]);
        printf("%lld\n",excrt());
    }
    return 0;
}