/in/foo.cc:15:5: warning: second argument of 'int main(int, char*)' should be 'char **' [-Wmain]
 int main(int argc, char argv[])
     ^~~~
/in/foo.cc: In function 'int main(int, char*)':
/in/foo.cc:28:26: error: expression cannot be used as a function
 sum += sqrt((x1-x2)(x1-x2) + (y1-y2)*(y1-y2));
                          ^