a = [0,2,7,23,47,167,359,839,1367,1847,2207,3719,5039,7919,10607,11447,16127,17159,19319,29927,36479,44519,49727,54287,57119,66047,85847,97967,113567,128879,177239,196247,201599,218087,241079,273527,292679,323759,344567,368447,426407,458327].reverse
b = [0,1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81].reverse
n = gets.to_i
a.each_with_index do |num,i|
    if num <= n
        puts b[i]
        exit
    end
end