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#include <iostream>

int main() {
	int n;
	std::cin >> n;

	std::string s;
	std::cin >> s;

	int zeroes = 0;
	int ones = 0;
	for (auto c: s) {
		if (c == '0') {
			++zeroes;
		} else {
			++ones;
		}
	}

	if ((zeroes - ones)&1) {
		puts("NIE\n");
		return 0;
	}

	if (zeroes > ones) {
		if ((zeroes - ones) / 2 > n) {
			puts("NIE\n");
		} else {
			std::string result((zeroes - ones) / 2, 'a');
			result += std::string(n - result.length(), 'c');
			std::cout << result << '\n';
		}
	} else {
		if ((ones - zeroes + 2) / 4 > n) {
			puts("NIE\n");
		} else {
			std::string result((ones - zeroes) / 4, 'w');
			if ((ones - zeroes) % 4 == 2) {
				result += 'z';
			}
			result += std::string(n - result.length(), 'c');
			std::cout << result << '\n';
		}
	}

	return 0;
}