#include <iostream>
using namespace std;

const int MOD = 1e9 + 7;
int mad(int u, int v) {
    u += v - MOD;
    u += MOD & (u >> 31);
    return u;
}

const int kN = 2002;
int N;
string S;
int dp[kN][kN];

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    cin >> N >> S;

    S = ' ' + S;
    dp[0][0] = 1;
    for (int i = 1; i <= N; ++i) {
        if (S[i] == '[' or S[i] == '?')
            for (int j = 1; j <= i; ++j)
                dp[i][j] = mad(dp[i][j], dp[i-1][j-1]);
        if (S[i] == ']' or S[i] == '?')
            for (int j = 0; j <= i; ++j)
                dp[i][j] = mad(dp[i][j], dp[i-1][j+1]);
    }

    cout << dp[N][0] << '\n';

    return 0;
}