#include <iostream>
#include <string>
#include <vector>


struct StorageBox {
	
	static const long long mod = 1000000007LL;
	
	static long long dp(const std::string &s) {
		std::vector<long long> count(s.size()+1);
		count[0] = 1;
		for (int i = 0; i < s.size(); ++i) {
			if (s[i] == '[') {
				for (int j = count.size()-1; j > 0; --j) {
					count[j] = count[j-1];
				}
				count[0] = 0;
			}
			else if (s[i] == ']') {
				for (int j = 0; j < count.size()-1; ++j) {
					count[j] = count[j+1];
				}
				count[count.size()-1] = 0;
			}
			else if (s[i] == '?') {
				std::vector<long long> count_tmp(count.size());
				for (int j = 1; j < count.size()-1; ++j) {
					count_tmp[j] = (count[j-1]+count[j+1])%mod;
				}
				count_tmp[0] = count[1];
				count_tmp[count.size()-1] = count[count.size()-2];
				count.swap(count_tmp);
			}
		}
		return count[0];
	}
	
};


int main() {
	
	std::cin.tie(nullptr);
	std::ios::sync_with_stdio(false);
	
	int N;
	std::string s;
	
	std::cin >> N;
	std::cin >> s;
	
	std::cout << StorageBox::dp(s) << '\n';
	
}