func factional(_ n: Int ) -> Int {
  if( n < 2 ) {
    return 1
  } else {
    return n * factional( n - 2 )
  }
}

let n=Int(readLine()!)!

let ret = factional(n)
let s = String(ret)

var c = 0
for ch in s.characters {
  if( ch == "0" ) {
    c += 1
  } else {
    c = 0
  }
}

print(c)

