#include

int gcd( int a, int b ){
  return b ? gcd( b, a%b ) : a;
}

int main () {
  int n, L, g=0;
  cin >> n;
  while( cin >> L ) g=gcd( L, g );
  cout << g << endl;
}

include what?
gcd is wrong too!

#include <iostream>
using namespace std;

int gcd( int a, int b )
{
return b ? gcd( b, a%b ) : a;
}

int main ()
{
int n, L, g=0;

cin >> n;

while( cin >> L ) g=gcd( L, g );
cout << g << endl;
}

Change your code to this and it runs perfectly!

Not complited first line, i suppose:

#include (what??)