HDU 1788 Chinese remainder theorem again

//1788
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#define LL long long

using namespace std ;

LL gcd(LL x,LL y)
{
return y == 0 ? x : gcd(y,x%y) ;
}
int main()
{
int I,a ;
while(~scanf("%d %d",&I,&a))
{
if(I == 0 && a == 0) break ;
int x ;
LL ans = 1;
while(I--)
{
scanf("%d",&x) ;
ans = (ans * x)/gcd(ans,x) ;
}
printf("%I64d\n",ans-a) ;
}
return 0 ;
}