#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<cstring>
#include<vector>
#include<list>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<stack>
using namespace std;
typedef long long ll;
#define fi first
#define se second
#define mp make_pair
#define rep(i, n) for(int i=0;i<n;++i)
#define rrep(i, n) for(int i=n;i>=0;--i)
const int inf=1e9+7;
const ll mod=1e9+7;
const ll mod1=998244353;
const ll big=1e18;
const double PI=2*asin(1);

ll mypow(ll a, ll b) {
  ll ans = 1;
  for(int i=0;i<b;++i) ans *= a;
  return ans;
}

int main() {
  ll A;
  cin>>A;
  bool can;
  ll ans=-1;
  for(ll m=1;m<=1000;++m) {
    can = false;
    for(ll i=1;i<=m;++i) {
      if(m%i!=0) continue;
      if(mypow(i, m/i)>=A) can = true;
    }
    if(can) {
      ans = m;
      break;
    }
  }
  cout<<ans<<endl;
}