#include <bits/stdc++.h>
using namespace std;
void readi(int &x) {
  int v = 0, f = 1;
  char c = getchar();
  while (!isdigit(c) && c != '-') c = getchar();
  if (c == '-')
    f = -1;
  else
    v = v * 10 + c - '0';
  while (isdigit(c = getchar())) v = v * 10 + c - '0';
  x = v * f;
}
void readll(long long &x) {
  long long v = 0ll, f = 1ll;
  char c = getchar();
  while (!isdigit(c) && c != '-') c = getchar();
  if (c == '-')
    f = -1;
  else
    v = v * 10 + c - '0';
  while (isdigit(c = getchar())) v = v * 10 + c - '0';
  x = v * f;
}
void readc(char &x) {
  char c;
  while ((c = getchar()) == ' ')
    ;
  x = c;
}
void writes(string s) { puts(s.c_str()); }
void writeln() { writes(""); }
void writei(int x) {
  if (!x) putchar('0');
  char a[25];
  int top = 0;
  while (x) {
    a[++top] = (x % 10) + '0';
    x /= 10;
  }
  while (top) {
    putchar(a[top]);
    top--;
  }
}
void writell(long long x) {
  if (!x) putchar('0');
  char a[25];
  int top = 0;
  while (x) {
    a[++top] = (x % 10) + '0';
    x /= 10;
  }
  while (top) {
    putchar(a[top]);
    top--;
  }
}
inline long long inc(int &x) { return ++x; }
inline long long inc(long long &x) { return ++x; }
inline long long inc(int &x, long long y) { return x += y; }
inline long long inc(long long &x, long long y) { return x += y; }
inline double inc(double &x, double y) { return x += y; }
inline long long dec(int &x) { return --x; }
inline long long dec(long long &x) { return --x; }
inline long long dec(int &x, long long y) { return x -= y; }
inline long long dec(long long &x, long long y) { return x -= y; }
inline double dec(double &x, double y) { return x -= y; }
inline long long mul(int &x) { return x = ((long long)x) * x; }
inline long long mul(long long &x) { return x = x * x; }
inline long long mul(int &x, long long y) { return x *= y; }
inline long long mul(long long &x, long long y) { return x *= y; }
inline double mul(double &x, double y) { return x *= y; }
inline long long divi(int &x) { return x = sqrt(x); }
inline long long divi(long long &x) { return x = sqrt(x); }
inline long long divi(int &x, long long y) { return x /= y; }
inline long long divi(long long &x, long long y) { return x /= y; }
inline double divi(double &x, double y) { return x /= y; }
inline long long mod(int &x, long long y) { return x %= y; }
inline long long mod(long long &x, long long y) { return x %= y; }
int dx[5] = {0, -1, 1, 0, 0}, dy[5] = {0, 0, 0, -1, 1};
string dc = "^v<>";
int n, m, i, j, k, dg[2222][2222];
queue<int> qx, qy;
char mp[2222][2222];
vector<pair<int, int> > add(int x, int y, int z) {
  int i;
  vector<pair<int, int> > ans;
  if ((1) <= ((4)))
    for (((i)) = (1); ((i)) <= ((4)); ((i))++) {
      dg[x + dx[i]][y + dy[i]] += z;
      if (dg[x + dx[i]][y + dy[i]] == 1 && mp[x + dx[i]][y + dy[i]] == '.')
        ans.push_back(make_pair(x + dx[i], y + dy[i]));
    }
  return ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  ;
  cin >> n >> m;
  if ((1) <= ((n)))
    for (((i)) = (1); ((i)) <= ((n)); ((i))++)
      if ((1) <= ((m)))
        for (((j)) = (1); ((j)) <= ((m)); ((j))++) cin >> mp[i][j];
  if ((1) <= ((n)))
    for (((i)) = (1); ((i)) <= ((n)); ((i))++)
      if ((1) <= ((m)))
        for (((j)) = (1); ((j)) <= ((m)); ((j))++)
          if (mp[i][j] == '.') add(i, j, 1);
  if ((1) <= ((n)))
    for (((i)) = (1); ((i)) <= ((n)); ((i))++)
      if ((1) <= ((m)))
        for (((j)) = (1); ((j)) <= ((m)); ((j))++)
          if (mp[i][j] == '.' && dg[i][j] == 1) {
            qx.push(i);
            qy.push(j);
          }
  while (!qx.empty()) {
    int x = qx.front(), y = qy.front();
    qx.pop();
    qy.pop();
    if (mp[x][y] != '.') continue;
    if ((1) <= ((4)))
      for (((k)) = (1); ((k)) <= ((4)); ((k))++) {
        if (mp[x + dx[k]][y + dy[k]] == '.') {
          mp[x][y] = dc[(k - 1) ^ 1];
          mp[x + dx[k]][y + dy[k]] = dc[(k - 1)];
          vector<pair<int, int> > nxt = add(x, y, -1);
          for (__typeof((nxt).begin()) it = (nxt).begin(); it != (nxt).end();
               it++) {
            if (mp[it->first][it->second] == '.') {
              qx.push(it->first);
              qy.push(it->second);
            }
          }
          nxt = add(x + dx[k], y + dy[k], -1);
          for (__typeof((nxt).begin()) it = (nxt).begin(); it != (nxt).end();
               it++) {
            if (mp[it->first][it->second] == '.') {
              qx.push(it->first);
              qy.push(it->second);
            }
          }
          break;
        }
      }
  }
  if ((1) <= ((n)))
    for (((i)) = (1); ((i)) <= ((n)); ((i))++)
      if ((1) <= ((m)))
        for (((j)) = (1); ((j)) <= ((m)); ((j))++)
          if (mp[i][j] == '.') {
            cout << "Not unique";
            return 0;
          };
  if ((1) <= ((n)))
    for (((i)) = (1); ((i)) <= ((n)); ((i))++) {
      if ((1) <= ((m)))
        for (((j)) = (1); ((j)) <= ((m)); ((j))++) cout << mp[i][j];
      cout << endl;
    }
  return 0;
}
