/in/foo.cc: In function 'LL solve(int, int, int, LL)':
/in/foo.cc:40:18: error: 'n' was not declared in this scope
  for(i = 0; i <= n; ++i) {
                  ^
/in/foo.cc:52:13: error: 'n' was not declared in this scope
   while(i < n) {
             ^
/in/foo.cc:29:5: warning: unused variable 'sum' [-Wunused-variable]
  LL sum = 0;
     ^~~
/in/foo.cc:30:9: warning: unused variable 'j' [-Wunused-variable]
  int i, j, l;
         ^