#include <bits/stdc++.h>
using namespace std;
inline long long getint() {
  long long _x = 0, _tmp = 1;
  char _tc = getchar();
  while ((_tc < '0' || _tc > '9') && _tc != '-') _tc = getchar();
  if (_tc == '-') _tc = getchar(), _tmp = -1;
  while (_tc >= '0' && _tc <= '9') _x *= 10, _x += (_tc - '0'), _tc = getchar();
  return _x * _tmp;
}
inline long long add(long long _x, long long _y,
                     long long _mod = 1000000007ll) {
  long long _ = _x + _y;
  if (_ >= _mod) _ -= _mod;
  return _;
}
inline long long sub(long long _x, long long _y,
                     long long _mod = 1000000007ll) {
  long long _ = _x - _y;
  if (_ < 0) _ += _mod;
  return _;
}
inline long long mul(long long _x, long long _y,
                     long long _mod = 1000000007ll) {
  long long _ = _x * _y;
  if (_ >= _mod) _ %= _mod;
  return _;
}
long long mypow(long long _a, long long _x, long long _mod) {
  if (_x == 0) return 1ll;
  long long _tmp = mypow(_a, _x / 2, _mod);
  _tmp = mul(_tmp, _tmp, _mod);
  if (_x & 1) _tmp = mul(_tmp, _a, _mod);
  return _tmp;
}
long long mymul(long long _a, long long _x, long long _mod) {
  if (_x == 0) return 0ll;
  long long _tmp = mymul(_a, _x / 2, _mod);
  _tmp = add(_tmp, _tmp, _mod);
  if (_x & 1) _tmp = add(_tmp, _a, _mod);
  return _tmp;
}
inline bool equal(double _x, double _y) {
  return _x > _y - 1e-9 && _x < _y + 1e-9;
}
int __ = 1, _cs;
void build() {}
long long m;
void init() { m = getint(); }
inline long long cal(long long x) {
  long long aa = 0;
  for (long long p = 2;; p++) {
    long long rp = p;
    bool fine = true;
    for (long long i = 0; i < 2; i++) {
      if (rp > x / p) fine = false;
      rp *= p;
    }
    if (!fine) break;
    aa += x / rp;
  }
  return aa;
}
inline long long bs() {
  long long bl = 8, br = 10000000000000000ll, bmid = -1, ba = -1;
  while (bl <= br) {
    bmid = (bl + br) >> 1;
    long long res = cal(bmid);
    if (res < m)
      bl = bmid + 1;
    else if (res > m)
      br = bmid - 1;
    else {
      br = bmid - 1;
      ba = bmid;
    }
  }
  return ba;
}
void solve() { printf("%lld\n", bs()); }
int main() {
  build();
  while (__--) {
    init();
    solve();
  }
}
