#include <bits/stdc++.h>
using namespace std;
char ans[1005][1005];
int x[1005][1005], y[1005][1005];
int n;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
bool isvalid(int i, int j) {
  if (i < 0 || j < 0 || i >= n || j >= n) return 0;
  return 1;
}
void color(int i, int j) {
  if (i < 0 || j < 0 || i >= n || j >= n || ans[i][j] == 'Z' || x[i][j] != -1 ||
      y[i][j] != -1)
    return;
  ans[i][j] = 'Z';
  for (int k = 0; k < 4; k++) color(i + dx[k], j + dy[k]);
}
void DFS(int i, int j, char ch, int ka, int kh) {
  if (i < 0 || j < 0 || i >= n || j >= n || x[i][j] == -1 || ans[i][j] != 'K')
    return;
  ans[i][j] = ch;
  if (isvalid(i + 1, j) && x[i + 1][j] == ka && y[i + 1][j] == kh) {
    DFS(i + 1, j, 'U', ka, kh);
  }
  if (isvalid(i - 1, j) && x[i - 1][j] == ka && y[i - 1][j] == kh) {
    DFS(i - 1, j, 'D', ka, kh);
  }
  if (isvalid(i, j + 1) && x[i][j + 1] == ka && y[i][j + 1] == kh) {
    DFS(i, j + 1, 'L', ka, kh);
  }
  if (isvalid(i, j - 1) && x[i][j - 1] == ka && y[i][j - 1] == kh) {
    DFS(i, j - 1, 'R', ka, kh);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> x[i][j] >> y[i][j];
      ans[i][j] = 'K';
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (x[i][j] == -1 && y[i][j] == -1)
        color(i, j);
      else if (x[i][j] == i + 1 && y[i][j] == j + 1)
        DFS(i, j, 'X', i + 1, j + 1);
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (ans[i][j] == 'Z') {
        if (isvalid(i + 1, j) && x[i + 1][j] == -1) {
          ans[i][j] = 'D';
          ans[i + 1][j] = 'U';
        } else if (isvalid(i - 1, j) && x[i - 1][j] == -1) {
          ans[i][j] = 'U';
          ans[i - 1][j] = 'D';
        } else if (isvalid(i, j + 1) && x[i][j + 1] == -1) {
          ans[i][j] = 'R';
          ans[i][j + 1] = 'L';
        } else if (isvalid(i, j - 1) && x[i][j - 1] == -1) {
          ans[i][j] = 'L';
          ans[i][j - 1] = 'R';
        }
      }
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (ans[i][j] == 'K' || ans[i][j] == 'Z') {
        cout << "INVALID";
        return 0;
      }
    }
  }
  cout << "VALID\n";
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) cout << ans[i][j];
    cout << "\n";
  }
  return 0;
}
