//括号匹配的问题
#include<iostream>
#include<stack>
using namespace std;
int main()
{
string c;
cin >> c;
stack<char> s1;
int flag;
for (int i = 0; i < c.size(); i++) {
flag = 0;
if (c[i] == '{' || c[i] == '[' || c[i] == '(') {
s1.push(c[i]);
}
else if (!s1.empty()) {
if (c[i] == ']' && s1.top()=='[') {
s1.pop();
}
else if (c[i] == '}' && s1.top() == '{') {
s1.pop();
}
else if (c[i] == ')' && s1.top() == '(') {
s1.pop();
}
else if (c[i] == ']' && s1.top() != '[') {
flag = 1;
break;
}
else if (c[i] == '}' && s1.top() != '{') {
flag = 1;
break;
}
else if (c[i] == ')' && s1.top() != '(') {
flag = 1;
break;
}
}
else if (c[i]=='}'||c[i]==']'||c[i]==')') {
flag = 1;
break;
}
else {
continue;
}
}
if (!s1.empty()) {
flag = 1;
}
if (flag == 0) {
cout << "ok" << endl;
}
else {
cout << "error" << endl;
}
return 0;
}