#include <bits/stdc++.h>
using namespace std;
vector<char> stek;
int main() {
  string str;
  bool solving = true;
  cin >> str;
  int xx;
  int oper = 0;
  int opened = 0;
  int closed = 0;
  int x = 0;
  for (int i = 0; i < str.length(); i++) {
    if (str[i] == '{' || str[i] == '[' || str[i] == '<' || str[i] == '(') {
      x++;
    } else {
      x--;
    }
    if (x < 0) {
      solving = false;
    }
  }
  if (x != 0) {
    solving = false;
  }
  if (!solving) {
    cout << "Impossible" << endl;
    return 0;
  } else {
    for (int i = 0; i < str.length(); i++) {
      if (str[i] == '{' || str[i] == '[' || str[i] == '<' || str[i] == '(') {
        if (str[i] == '{') stek.push_back(1);
        if (str[i] == '[') stek.push_back(2);
        if (str[i] == '<') stek.push_back(3);
        if (str[i] == '(') stek.push_back(4);
      } else if (str[i] == '}' || str[i] == ']' || str[i] == '>' ||
                 str[i] == ')') {
        if (str[i] == '}') xx = 1;
        if (str[i] == ']') xx = 2;
        if (str[i] == '>') xx = 3;
        if (str[i] == ')') xx = 4;
        int temp = stek.back();
        stek.pop_back();
        if (temp != xx) {
          oper++;
        }
      }
    }
    cout << oper << endl;
  }
  return 0;
}
