信奥一本通1354，第五个点运行错误

#include<bits/stdc++.h>
using namespace std;

stack<char> a;
string s;

int main()
{
	cin>>s;
	for(int i=0;i<s.size();i++){
		if(s[i]=='('||s[i]=='[')a.push(s[i]);
		else{
			if(s[i]==')')
				if(a.top()=='(')a.pop();
				else{
					cout<<"Wrong"<<endl;
					return 0;
				}
			else if(s[i]==']')
				if(a.top()=='[')a.pop();
				else{
					cout<<"Wrong"<<endl;
					return 0;
				}
		}
	}
	if(a.empty()==false)cout<<"Wrong"<<endl;
	else cout<<"OK"<<endl;
	return 0;
}