import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

void main() {
    int x = readint;

    int ans = 1;
    for (int b = 2; b <= x; b++) {
        int a = b * b;
        while (a <= x) {
            ans = max(ans, a);
            a *= b;
        }
    }
    writeln(ans);
}
