n = gets.to_i
f = [1]
if n%2 == 0
  [*1..n/2].each{|i|
    f << 2*i*f[i-1]
  }
else
  [*1..n/2+1].each{|i|
    f << (2*i-1)*f[i-1]
  }
end
fn = f.pop
fnc = fn.to_s.chars
ans = 0
while fnc.pop == '0'
  ans += 1
end
p ans