#include <bits/stdc++.h>
using namespace std;
unsigned long long _pow(unsigned long long x,unsigned long long y){
	int sum=1;
	for(int i=1;i<=y;i++)
		sum*=x;
	return sum;
}
int main() {
	unsigned long long a, i = 1;
	cin >> a;
	for (; _pow(i, i) <= a; i++) {};
	i--;
	if (_pow(i, i) == a)
		cout << i;
	else
		cout << "-1";
	cout << "\n";
	return 0;
}

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