#include <iostream>
#include <string>

inline int index_by_letter(char c)
{
	int i = 0;
	switch (c)
	{
		case 'M':
			++i;
		case 'D':
			++i;
		case 'C':
			++i;
		case 'L':
			++i;
		case 'X':
			++i;
		case 'V':
			++i;
	}
	return i;
}

const int value_by_index[7] = {1, 5, 10, 50, 100, 500, 1000};
int count[7] = {0, 0, 0, 0, 0, 0, 0};
int solution[7] = {0, 0, 0, 0, 0, 0, 0};
const char *letter_by_index = "IVXLCDM";
int max_index = 6;
int n;
int input_value_without_max = 0;

inline int calculate()
{
	return solution[0] * value_by_index[0] + solution[1] * value_by_index[1] + solution[2] * value_by_index[2] +
		solution[3] * value_by_index[3] + solution[4] * value_by_index[4] + solution[5] * value_by_index[5] + solution[6] * value_by_index[6];
}

bool solve(int current_depth)
{
	if (++current_depth == max_index)
	{
		return n + input_value_without_max == 2 * calculate();
	}
	for (int i = 0; i <= count[current_depth]; ++i)
	{
		solution[current_depth] = i;
		if (solve(current_depth))
		{
			return true;
		}
	}
	return false;
}

int main()
{
	std::string s;
	std::cin >> n >> s;
	for (auto c: s)
	{
		++count[index_by_letter(c)];
	}
	for (; max_index > 0 && !count[max_index]; --max_index);
	n -= count[max_index] * value_by_index[max_index];
	for (int i = 0; i < max_index; input_value_without_max += value_by_index[i] * count[i], ++i);
	if (solve(-1))
	{
		for (int i = max_index; i > 0; )
		{
			--i;
			std::cout << std::string(count[i] - solution[i], letter_by_index[i]);
		}
		std::cout << std::string(count[max_index], letter_by_index[max_index]);
		for (int i = max_index; i > 0; )
		{
			--i;
			std::cout << std::string(solution[i], letter_by_index[i]);
		}
		std::cout << std::endl;
	}
	else
	{
		std::cout << "NO" << std::endl;
	}
	return 0;
}