#include <stdio.h>

#define N 1000

int posl[N];
int n;

int main(void)
  {
    int i, f_nneg;
    int x, x2, x3;
    int xna2, xna3;

    scanf("%d", &n);
    for (i = 0; i < n; i++)
      scanf("%d", posl + i);

    for (f_nneg = 0; f_nneg < n; f_nneg++)
      if (posl[f_nneg] >= 0)
        break;

    /* Nezaporna cisla.  */
    for (x = x2 = x3 = f_nneg; x3 < n; x++)
      {
        xna2 = posl[x] * posl[x];
	xna3 = xna2 * posl[x];

        while (x2 < n && xna2 > posl[x2]) x2++;
        while (x3 < n && xna3 > posl[x3]) x3++;

        if (xna2 == posl[x2] && xna3 == posl[x3])
          goto found;
      }

    /* Zaporna cisla.  */
    for (x = x3 = f_nneg - 1, x2 = f_nneg; x3 >= 0 && x2 < n; x--)
      {
        xna2 = posl[x] * posl[x];
	xna3 = xna2 * posl[x];

        while (x2 < n && xna2 > posl[x2]) x2++;
        while (x3 >= 0 && xna3 < posl[x3]) x3--;

        if (xna2 == posl[x2] && xna3 == posl[x3])
          goto found;
      }

    printf ("Takove x neexistuje.\n");
    return 0;

    found:
    printf ("Nalezena cisla %d, %d, %d.\n", posl[x], posl[x2], posl[x3]);
    return 0;
  }