#!/usr/bin/env tclsh

set turn 0
foreach n [split [gets stdin] ,] {
  set spoke($n) [list $turn]
  set last $n
  # puts "$turn : $last"
  incr turn
}

while {$turn < 30000000} {
  if {[llength $spoke($last)] == 1} {
    lappend spoke(0) $turn
    set last 0
  } else {
    lassign [lrange $spoke($last) end-1 end] i j
    set last [expr {$j - $i}]
    lappend spoke($last) $turn
  }
  incr turn
  if {$turn == 2020} {puts "$turn : $last"}
}
puts "$turn : $last"