#include <bits/stdc++.h>
using namespace std;
template <typename T>
T in() {
  char ch;
  T n = 0;
  bool ng = false;
  while (1) {
    ch = getchar();
    if (ch == '-') {
      ng = true;
      ch = getchar();
      break;
    }
    if (ch >= '0' && ch <= '9') break;
  }
  while (1) {
    n = n * 10 + (ch - '0');
    ch = getchar();
    if (ch < '0' || ch > '9') break;
  }
  return (ng ? -n : n);
}
template <typename T>
inline T Dis(T x1, T y1, T x2, T y2) {
  return sqrt((x1 - x2 * x1 - x2) + (y1 - y2 * y1 - y2));
}
template <typename T>
inline T POW(T B, T P) {
  if (P == 0) return 1;
  if (P & 1)
    return B * POW(B, P - 1);
  else
    return (POW(B, P / 2) * POW(B, P / 2));
}
template <typename T>
inline T ABS(T a) {
  if (a < 0)
    return -a;
  else
    return a;
}
template <typename T>
inline T Gcd(T a, T b) {
  if (a < 0) return Gcd(-a, b);
  if (b < 0) return Gcd(a, -b);
  return (b == 0) ? a : Gcd(b, a % b);
}
template <typename T>
inline T Lcm(T a, T b) {
  if (a < 0) return Lcm(-a, b);
  if (b < 0) return Lcm(a, -b);
  return a * (b / Gcd(a, b));
}
long long Bigmod(long long base, long long power, long long MOD) {
  long long ret = 1;
  while (power) {
    if (power & 1) ret = (ret * base) % MOD;
    base = (base * base) % MOD;
    power >>= 1;
  }
  return ret;
}
long long ModInverse(long long number, long long MOD) {
  return Bigmod(number, MOD - 2, MOD);
}
int Set(int N, int pos) { return N = N | (1 << pos); }
int Reset(int N, int pos) { return N = N & ~(1 << pos); }
bool Chkbit(int N, int pos) { return (bool)(N & (1 << pos)); }
bool isVowel(char ch) {
  ch = toupper(ch);
  if (ch == 'A' || ch == 'U' || ch == 'I' || ch == 'O' || ch == 'E')
    return true;
  return false;
}
bool isConst(char ch) {
  if (isalpha(ch) && !isVowel(ch)) return true;
  return false;
}
int toInt(string s) {
  int sm;
  stringstream ss(s);
  ss >> sm;
  return sm;
}
long long int toLlint(string s) {
  long long int sm;
  stringstream ss(s);
  ss >> sm;
  return sm;
}
int ar[2005][2005], br[2005][2005], Ind[2005][2005];
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
string s[2005], S[2005];
int n, m;
void Solve(int x, int y, int xx, int yy) {
  y--, yy--;
  if (x > xx) {
    swap(x, xx);
    swap(y, yy);
  } else if (y > yy) {
    swap(y, yy);
  }
  if (x == xx) {
    s[x][y] = '<', s[xx][yy] = '>';
  } else {
    s[x][y] = '^', s[xx][yy] = 'v';
  }
  return;
}
int main() {
  cin >> n >> m;
  int id = 1, Cnt = 0;
  for (int i = 1; i < n + 1; i++) {
    cin >> s[i];
    S[i] = s[i];
    for (int j = 0; j < m; j++) {
      if (s[i][j] == '.') ar[i][j + 1] = 1, Cnt++;
    }
  }
  queue<int> Q;
  for (int i = 1; i < n + 1; i++) {
    for (int j = 1; j < m + 1; j++) {
      if (!ar[i][j]) continue;
      int x = i, y = j;
      int T = 0;
      for (int k = 0; k < 4; k++) {
        int xx = x + dx[k], yy = y + dy[k];
        if (xx >= 1 && xx <= n && yy >= 1 && yy <= m && ar[xx][yy]) T++;
      }
      Ind[x][y] = T;
      if (T == 1) Q.push(x), Q.push(y);
    }
  }
  while (Q.size()) {
    int x = Q.front();
    Q.pop();
    int y = Q.front();
    Q.pop();
    int f = 0;
    for (int i = 0; i < 4; i++) {
      int xx = x + dx[i], yy = y + dy[i];
      if (xx >= 1 && xx <= n && yy >= 1 && yy <= m && ar[xx][yy]) {
        f = 1;
        Ind[x][y] = 0, Ind[xx][yy] = 0;
        ar[x][y] = 0, ar[xx][yy] = 0;
        Cnt -= 2;
        Solve(x, y, xx, yy);
        for (int j = 0; j < 4; j++) {
          int xxx = xx + dx[j], yyy = yy + dy[j];
          if (xx >= 1 && xx <= n && yy >= 1 && yy <= m && ar[xxx][yyy]) {
            Ind[xxx][yyy]--;
            if (Ind[xxx][yyy] == 1) {
              Q.push(xxx), Q.push(yyy);
            }
          }
        }
        break;
      }
    }
    if (!Cnt) break;
  }
  if (Cnt) {
    printf("Not unique\n");
    return 0;
  }
  for (int i = 1; i < n + 1; i++) {
    cout << s[i] << endl;
  }
  return 0;
}
