#include <bits/stdc++.h>
int main() {
  int n, t, vector[50], m, i, bandera = 0, a, b, c, dif, dif2, dif3;
  scanf("%d", &n);
  if (n < 3 || n > 50) {
    do {
      printf("Valor incorrecto. Vuelva a intentarlo\n");
      scanf("%d", &n);
    } while (n < 3 || n > 50);
  }
  for (i = 0; i < n; i++) {
    scanf("%d", &t);
    if (t < 1 || t > 1000) {
      do {
        printf("Valor incorrecto. Vuelva a intentarlo\n");
        scanf("%d", &t);
      } while (n < 3 || n > 50);
    }
    vector[i] = t;
  }
  for (a = 0; a < n - 2; a++) {
    for (b = a + 1; b < n - 1; b++) {
      for (c = b + 1; c < n; c++) {
        dif = abs(vector[a] - vector[b]);
        dif2 = abs(vector[a] - vector[c]);
        dif3 = abs(vector[c] - vector[b]);
        if (dif < 3 && dif2 < 3 && dif3 < 3 && vector[a] != vector[b] &&
            vector[a] != vector[c] && vector[b] != vector[c] && bandera != 1) {
          printf("YES");
          bandera = 1;
        }
      }
    }
  }
  if (bandera != 1) {
    printf("NO");
  }
  return 0;
}
