n,m = gets.split.map(&:to_i)
x,y = gets.split.map(&:to_f)

a=(((x+1)/m).round)%2
b=(((y+1)/m).round)%2
if n <= m then
    puts "NO\n"
    exit
end
if (a==b) && (x%m==0) && (y%m==0) then
    puts "YES\n"
else
    newX=0
    newY=0
    if a==0 then
        newX=(x-1)%m
        newY=y%m
    else
        newX=x%m
        newY=(y-1)%m
    end
    if newX==newY then
        puts "YES\n"
    else
        puts "NO\n"
    end
end