View Compilation Error

0_0_18434974_26529.cpp: In function 'int main()':
0_0_18434974_26529.cpp:33:17: error: unable to find numeric literal operator 'operator""k'
    for (int i = 2k - 1; i > k; --i)
                 ^
0_0_18434974_26529.cpp:33:17: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes