View Compilation Error

0_0_25108006_1331.cpp: In function 'int main()':
0_0_25108006_1331.cpp:29:45: error: unable to find numeric literal operator 'operator""a'
             input.erase(input.length() - 1, 1a);
                                             ^
0_0_25108006_1331.cpp:29:45: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes