import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  int x; readV(x);

  auto m = 1;
  foreach (b; 2..x.nsqrt+1)
    foreach (p; 2..10) {
      auto c = b^^p;
      if (c > x) break;
      m = max(m, c);
    }

  writeln(m);
}

pure T nsqrt(T)(T n)
{
  import std.algorithm, std.conv, std.range, core.bitop;
  if (n <= 1) return n;
  T m = T(1) << (n.bsr/2+1);
  return iota(1, m).map!"a * a".assumeSorted!"a <= b".lowerBound(n).length.to!T;
}
