Store path
vector < int > path ; path . push_back ( N ) ; while ( ind > 1 ) { ll val = temp - prefix [ ind - 1 ] ; if ( ind % 2 != 0 ) { temp = prefix [ ind - 2 ] + ( val + 1 ) / 2 ; } else { temp = prefix [ ind - 2 ] + ( val + 3 ) / 4 ; } -- ind ;