import java.util.*;

class Main{
	
	public static void main(String args[]){

		Scanner sc = new Scanner(System.in);

		int X = sc.nextInt();
		
		int max=1;
		for(int t=2;t<=(int)Math.sqrt(X);t++){
			int s=1;
			while((int)Math.pow(t,s) <= X){
				s++;
			}
			if(max < (int)Math.pow(t,s-1)) max = (int)Math.pow(t,s-1);
		}

		System.out.println(max);
		
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz