#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T, class T1>
inline void gn(T &first, T1 &second) {
  gn(first);
  gn(second);
}
template <class T, class T1, class T2>
inline void gn(T &first, T1 &second, T2 &z) {
  gn(first);
  gn(second);
  gn(z);
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T>
inline void printsp(T first) {
  print(first);
  putchar(' ');
}
template <class T>
inline void println(T first) {
  print(first);
  putchar('\n');
}
template <class T, class U>
inline void print(T first, U second) {
  printsp(first);
  println(second);
}
template <class T, class U, class V>
inline void print(T first, U second, V z) {
  printsp(first);
  printsp(second);
  println(z);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
char a[2222][2222];
queue<pair<int, int> > q;
char T1[] = "<^>v";
char T2[] = ">v<^";
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
int main() {
  int n, m, first, second;
  gn(n, m);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) {
      scanf(" %c", &a[i][j]);
      if (a[i][j] == '.') q.push(pair<int, int>(i, j));
    }
  int cnt, dir, xx, yy;
  while (!q.empty()) {
    cnt = 0;
    first = q.front().first, second = q.front().second;
    q.pop();
    if (a[first][second] != '.') continue;
    for (int i = 0; i < 4; i++) {
      xx = first + dx[i], yy = second + dy[i];
      if ((xx < 0 or yy < 0 or xx >= n or yy >= m)) continue;
      if (a[xx][yy] != '.')
        continue;
      else
        cnt++, dir = i;
    }
    if (cnt != 1) continue;
    xx = first + dx[dir], yy = second + dy[dir];
    a[first][second] = T1[dir], a[xx][yy] = T2[dir];
    for (int i = 0; i < 4; i++) {
      int u = xx + dx[i], v = yy + dy[i];
      if ((u < 0 or v < 0 or u >= n or v >= m)) continue;
      if (u == first and v == second) continue;
      if (a[u][v] == '.') q.push(pair<int, int>(u, v));
    }
  }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
      if (a[i][j] == '.') return puts("Not unique");
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) putchar(a[i][j]);
    puts("");
  }
}
