//valid,6857
//:END:
import "../std.qbl"

600851475143 2 divHasLargerPF 3
while
{
	// n p
	req dup 2 req req +
	// p n p+2
	swp req
	// n p p+2
	divHasLargerPF
	// p+2 hasLPF newN
	req
}
deq 2 - intToStr println

function int int => bool int divHasLargerPF
{
	req dup req divIfDivisible
	// n newN
	1 req dup
	// newN 1 n newN
	== req req
	// is1 n newN
	if
	{
		false req deq
	}
	else
	{
		true deq req
	}
}

function int int => int divIfDivisible
{
	// p n
	dup req dup swp
	// p n p n
	divmod 0
	// p n p/n p%n 0
	req req req ==
	// p n p/n isDiv
	req req req
	if
	{
		deq req divIfDivisible
	}
	else
	{
		req deq deq
	}
}