#include <bits/stdc++.h>
using namespace std;
int match(char a, char b) {
  if (a == '[' && b == ']')
    return 1;
  else if (a == '{' && b == '}')
    return 1;
  else if (a == '(' && b == ')')
    return 1;
  else if (a == '<' && b == '>')
    return 1;
  else
    return 0;
}
int main() {
  string str;
  int count = 0, n = 0;
  stack<char> s;
  cin >> str;
  int len = (int)str.size();
  for (int i = 0; i < len; i++) {
    if (str[i] == '<' || str[i] == '{' || str[i] == '(' || str[i] == '[')
      s.push(str[i]);
    else {
      if (s.empty()) {
        n++;
        break;
      } else {
        char c = s.top();
        int k = match(c, str[i]);
        if (k == 1)
          s.pop();
        else {
          count++;
          s.pop();
        }
      }
    }
  }
  int p = s.empty();
  if (n > 0 || p == 0)
    cout << "Impossible";
  else
    cout << count;
}
