/in/foo.cc:2:2: error: invalid preprocessing directive #i3nclude
 #i3nclude <cmath>
  ^~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:17:35: error: 'pow' was not declared in this scope
    len += sqrt(pow(x[i] - x[i - 1]) + pow(y[i] - y[i - 1]));
                                   ^
/in/foo.cc:17:59: error: 'sqrt' was not declared in this scope
    len += sqrt(pow(x[i] - x[i - 1]) + pow(y[i] - y[i - 1]));
                                                           ^
/in/foo.cc:20:31: error: 'pow' was not declared in this scope
  len += sqrt(pow(x[n-1] - x[0]) + pow(y[0] - y[n - 1]));
                               ^
/in/foo.cc:20:55: error: 'sqrt' was not declared in this scope
  len += sqrt(pow(x[n-1] - x[0]) + pow(y[0] - y[n - 1]));
                                                       ^