Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<queue>

#include<cctype>

#include<cstring>

using namespace std;

inline char getc()

{

	register char c = getchar();

	while(c != '.' && c != '*')c = getchar();

	return c;

}

int n,m;

#define MAXN 2010

char c[MAXN][MAXN];

int deg[MAXN][MAXN];

int mx[4] = {0,0,1,-1};

int my[4] = {1,-1,0,0};

char cx[4] = {'<','>','^','v'};

char cy[4] = {'>','<','v','^'};

#define fi first

#define se second

int main()

{

	scanf("%d%d",&n,&m);

	for(int i = 1;i <= n;++i)

		for(int j = 1;j <= m;++j)

			c[i][j] = getc();

	for(int i = 1;i <= n;++i)

		for(int j = 1;j <= m;++j)

			for(int k = 0;k < 4;++k)

				if(c[i + mx[k]][j + my[k]] != 0 && c[i + mx[k]][j + my[k]] != '*')

					++deg[i][j];

	for(int i = 1;i <= n;++i)

	{

		for(int j = 1;j <= m;++j)

		{

			if(deg[i][j] == 0 && c[i][j] == '.')

			{

				puts("Not unique");

				return 0;

			}

		}

	}

	queue< pair<int,int> > q;

	for(int i = 1;i <= n;++i)

		for(int j = 1;j <= m;++j)

			if(c[i][j] == '.' && deg[i][j] == 1)

				q.push(make_pair(i,j));

	while(!q.empty())

	{

		pair<int,int> k = q.front();q.pop();

		for(int i = 0;i < 4;++i)

		{

			if(c[k.fi + mx[i]][k.se + my[i]] == '.')

			{

				c[k.fi][k.se] = cx[i];

				c[k.fi + mx[i]][k.se + my[i]] = cy[i];

				int xx = k.fi + mx[i],yy = k.se + my[i];

				for(int j = 0;j < 4;++j)

				{

					if(c[xx + mx[j]][yy + my[j]] == '.')

					{

						--deg[xx + mx[j]][yy + my[j]];

						if(deg[xx + mx[j]][yy + my[j]] == 1)

						{

							q.push(make_pair(xx + mx[j],yy + my[j]));

						}

					}

				}

			}

		}

	}

	for(int i = 1;i <= n;++i)

	{

		for(int j = 1;j <= m;++j)

		{

			if(c[i][j] == '.')

			{

				puts("Not unique");

				return 0;

			}

		}

	}

	for(int i = 1;i <= n;++i)

	{

		for(int j = 1;j <= m;++j)

		{

			putchar(c[i][j]);

		}

		puts("");

	}

	return 0;

}