import algorithm
import math
import strutils

const WindowSize = 3

proc countIncreases(): uint =
  var
    line = ""
    window: array[WindowSize + 1, uint]
  while readLine(stdin, line):
    if line.len() > 0:
      window.rotateLeft(1)
      window[^1] = parseUint(line)
      if window[0] > 0 and sum(window[1 .. ^1]) > sum(window[0 .. ^2]):
        result.inc()

proc main(): int =
  try:
    echo countIncreases()
  except ValueError:
    result = -1

when isMainModule:
  quit(main())