#include <iostream>

using namespace std;

#ifndef DEBUG
#define cerr err_debug
struct err_debug_t {
  template <class T>
  err_debug_t & operator << ( const T &x ) {
    return *this;
  }
} err_debug;
#endif

// Attention: DO NOT USE endl!
int main() { 
  cerr << 2 << "\n";
  cerr << "abc" << 3 << "\n";
}