/in/foo.cc: In function 'int main()':
/in/foo.cc:18:13: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
             if(f[k]==0) ans++;
             ^~
/in/foo.cc:19:4: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
    ++f[k];
    ^~
/in/foo.cc:8:14: warning: 'back' may be used uninitialized in this function [-Wmaybe-uninitialized]
  int n,front,back;
              ^~~~
/in/foo.cc:8:8: warning: 'front' may be used uninitialized in this function [-Wmaybe-uninitialized]
  int n,front,back;
        ^~~~~