N = gets.to_i

ok = 1
ng = N

while (ok - ng).abs >= 2
  x = (ok + ng) / 2

  if Rational(N, x) - Rational(N, x + 1) > 1
    ok = x
  else
    ng = x
  end
end 

puts ok + Rational(N, ok + 1).to_i