/in/foo.cc:6:1: error: 'LL' does not name a type
 LL a[N];
 ^~
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:28: error: 'a' was not declared in this scope
  for(int i=1;i<=n;i++)cin>>a[i];
                            ^
/in/foo.cc:15:8: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
  cin>>s+1;
       ~^~
/in/foo.cc:25:8: error: 'a' was not declared in this scope
      x=a[i]+a[i-1];
        ^
/in/foo.cc:27:8: error: 'a' was not declared in this scope
      y=a[i]+a[i+1];
        ^
/in/foo.cc:42:11: error: 'a' was not declared in this scope
      res+=a[i-1]+a[i];
           ^