HDU 1788——Chinese remainder theorem again

#include<cstdio>
#include<iostream>
using namespace std;
typedef long long ll;

ll m[15];

ll extend_gcd(ll a,ll b){
    if(b==0){
        return a;
    }
    else{
        ll r=extend_gcd(b,a%b);
        return r;
    }
}

int main(){
 //   freopen("data.txt","r",stdin);
    int I;
    ll a;
    while(scanf("%d%I64d",&I,&a)!=EOF){
   //         cout<<I<<' '<<a<<endl;
            if(I==0&&a==0)break;
        ll lcm;
        for(int i=0;i<I;++i){
            scanf("%I64d",&m[i]);
 //  cout<<m[i]<<endl;
            if(i==0){lcm=m[i];}
            else {//gcd=M/extend_gcd(gcd,m[i],x,y);
                lcm=(lcm*m[i])/extend_gcd(lcm,m[i]);
            }
        }
        ll ans=lcm-a;
        printf("%I64d\n",ans);
    }
    return 0;
}