import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;
import std.container;

alias sread = () => readln.chomp();
alias Point2 = Tuple!(long, "y", long, "x");

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

void main()
{
    long x = lread();
    long max_pow = 1;
    foreach (e; 2 .. 40)
    {
        long i = 2,j;
        while(1)
        {
            j = pow(e,i);
            i++;
            if(j > x)
            {
                break;
            }
            max_pow = max(j, max_pow);
        }
    }
    writeln(max_pow);
}