D

#include <bits/stdc++.h>

using namespace std;

#define int long long

const long long INF = 1e18 + 7;
const int MAXN = 1e2 + 100;
const int N = 1e5 + 10;

array<array<int, MAXN>, MAXN> dp, p;
string s;

bool match(char a, char b) {
    return a == '(' && b == ')' || a == '[' && b == ']' || a == '{' && b == '}';
}

void rec(int l, int r) {
//    cout << l << ' ' << r << endl;
    if (l > r || dp[l][r] == r - l + 1) {
        return;
    }
    if (p[l][r] != -INF) {
        rec(l, p[l][r]);
        rec(p[l][r] + 1, r);
    } else if (p[l][r] == -INF) {
        cout << s[l];
        rec(l + 1, r - 1);
        cout << s[r];
        return;
    }
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cin >> s;
    int n = s.size();
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            dp[i][j] = INF;
            p[i][j] = -INF;
        }
    }
    for (int i = 0; i < n - 1; ++i) {
        dp[i][i] = 1;
        dp[i][i + 1] = 2 * (!match(s[i], s[i + 1]));
    }
    dp[n - 1][n - 1] = 1;
    for (int len = 2; len < n; ++len) {
        for (int l = 0; l + len < n; ++l) {
            int r = l + len;
            dp[l][r] = dp[l + 1][r - 1] + (match(s[l], s[r])? 0 : INF);
            for (int m = l; m < r; ++m) {
                if (dp[l][r] > dp[l][m] + dp[m + 1][r]) {
                    dp[l][r] = dp[l][m] + dp[m + 1][r];
                    p[l][r] = m;
                }
            }
        }
    }

    rec(0, n - 1);
}