#include <bits/stdc++.h>
using namespace std;
const int N = 550;
int i, j, k, n, m, nm, ch;
int a[N][N];
struct cc {
  int x, y;
} A[N * N];
bool cmp1(const cc &a, const cc &b) {
  if (a.x == b.x) return a.y < b.y;
  return a.x < b.x;
}
bool cmp2(const cc &a, const cc &b) {
  int x1, y1, x2, y2;
  x1 = a.x - A[1].x;
  y1 = a.y - A[1].y;
  x2 = b.x - a.x;
  y2 = b.y - a.y;
  return x1 * y2 < x2 * y1;
}
int dis(const cc &a, const cc &b) {
  return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
}
bool cmp3(const cc &a, const cc &b) { return dis(A[1], a) < dis(A[1], b); }
bool cmp4(const cc &a, const cc &b) { return dis(A[1], a) > dis(A[1], b); }
bool check(const cc &a, const cc &b, const cc &c) {
  int x1, y1, x2, y2;
  x1 = b.x - a.x;
  y1 = b.y - a.y;
  x2 = c.x - b.x;
  y2 = c.y - b.y;
  if (x1 * y2 == x2 * y1) return dis(a, b) < dis(a, c);
  return x1 * y2 > x2 * y1;
}
bool check2(const cc &a, const cc &b, const cc &c) {
  int x1, y1, x2, y2;
  x1 = b.x - a.x;
  y1 = b.y - a.y;
  x2 = c.x - b.x;
  y2 = c.y - b.y;
  return x1 * y2 < x2 * y1;
}
bool check3(const cc &a, const cc &b, const cc &c) {
  int x1, y1, x2, y2;
  x1 = b.x - a.x;
  y1 = b.y - a.y;
  x2 = c.x - b.x;
  y2 = c.y - b.y;
  return x1 * y2 == x2 * y1;
}
int main() {
  scanf("%d", &n);
  while (n) {
    m = 0;
    for (i = 1; i <= n; i++) a[i][n + 1] = a[n + 1][i] = 0;
    a[n + 1][n + 1] = 0;
    for (j = n; j; j--)
      for (i = 1; i <= n; i++) {
        ch = getchar();
        while (ch < '0' || '4' < ch) ch = getchar();
        a[i][j] = ch - '0';
      }
    for (i = 1; i <= n; i++)
      for (j = 1; j <= n; j++)
        if (a[i][j] == 1) {
          if (!a[i + 1][j - 1] && !a[i + 1][j] && !a[i][j - 1])
            A[++m].x = i - 1, A[m].y = j;
          if (!a[i + 1][j + 1] && !a[i + 1][j] && !a[i][j + 1])
            A[++m].x = i - 1, A[m].y = j - 1;
          if (!a[i - 1][j + 1] && !a[i - 1][j] && !a[i][j + 1])
            A[++m].x = i, A[m].y = j - 1;
          if (!a[i - 1][j - 1] && !a[i - 1][j] && !a[i][j - 1])
            A[++m].x = i, A[m].y = j;
        }
    sort(A + 1, A + m + 1, cmp1);
    A[m + 1].x = -1;
    nm = 0;
    for (i = 1; i <= m; i++)
      if (A[i].x != A[i + 1].x || A[i].y != A[i + 1].y) A[++nm] = A[i];
    sort(A + 2, A + nm + 1, cmp2);
    i = 2;
    while (i < nm && check3(A[1], A[2], A[i + 1])) i++;
    sort(A + 2, A + i + 1, cmp3);
    i = nm;
    while (i > 2 && check3(A[1], A[nm], A[i - 1])) i--;
    sort(A + i + 1, A + nm + 1, cmp4);
    m = 2;
    for (i = 3; i <= nm; i++) {
      while (m >= 2 && check(A[m - 1], A[m], A[i])) m--;
      if (m < 2)
        A[++m] = A[i];
      else if (check2(A[m - 1], A[m], A[i]))
        A[++m] = A[i];
    }
    while (m >= 2 && check(A[m - 1], A[m], A[1])) m--;
    printf("%d\n", m);
    for (i = 1; i <= m; i++) printf("%d %d\n", A[i].x, A[i].y);
    scanf("%d", &n);
  }
}
