#3 和 #8 莫名RE，不知道为什么，有大佬帮忙看看吗

#include <iostream>
#include <string>
#include <cstdio>
using namespace std;
const int maxn = 1e6 + 5;
string str;
int s[maxn], top;
int vis[maxn];
int main() {
	cin >> str;
	int len = str.length();
	for (int i = 0; i < len; i++) {
		if (str[i] == '(' || str[i] == '[') {
			s[++top] = i;
		} else if (str[i] == ')') {
			if (str[s[top]] == '(') {
				vis[s[top]] = vis[i] = true;
				top--;
			} else {
				top = 0;
			}
		} else {
			if (str[s[top]] == '[') {
				vis[s[top]] = vis[i] = true;
				top--;
			} else {
				top = 0;
			}
		}
	}
	int ansl = 0, ansr = 0;
	for (int l = 0; l < len; l++) {
		int r = l;
		while (vis[r]) r++;
		if (r - l > ansr - ansl + 1) {
			ansl = l, ansr = r - 1;
		}
		l = r;
	}
	for (int i = ansl; i <= ansr; i++) {
		putchar(str[i]);
	}
	return 0;
}