#include <bits/stdc++.h>
using namespace std;
void open() { freopen("data.txt", "r", stdin); }
void out() { freopen("out.txt", "w", stdout); }
const int INF = 0x3f3f3f3f;
const int maxn = 1e6 + 5;
const int MOD = 1e9 + 7;
int id(char c) {
  if (c == '(') return 1;
  if (c == '[') return 2;
  if (c == '{') return 3;
  if (c == '<') return 4;
  if (c == ')') return 8;
  if (c == ']') return 7;
  if (c == '}') return 6;
  if (c == '>') return 5;
}
char str[maxn];
int main() {
  scanf("%s", str);
  int len = strlen(str);
  int cnt1 = 0, cnt2 = 0;
  for (int i = 0; i < (len); ++i) {
    if (str[i] == '(')
      cnt1++;
    else if (str[i] == '[')
      cnt1++;
    else if (str[i] == '{')
      cnt1++;
    else if (str[i] == '<')
      cnt1++;
    else if (str[i] == ']')
      cnt2++;
    else if (str[i] == '}')
      cnt2++;
    else if (str[i] == ')')
      cnt2++;
    else if (str[i] == '>')
      cnt2++;
  }
  if (cnt1 != cnt2) {
    puts("Impossible");
    return 0;
  }
  bool ok = true;
  int ans = 0;
  stack<int> s;
  for (int i = 0; i < (len); ++i) {
    int tmp = id(str[i]);
    if (s.empty()) {
      s.push(tmp);
      continue;
    }
    if (tmp <= 4) {
      s.push(tmp);
      continue;
    }
    if (tmp + s.top() == 9) {
      s.pop();
      continue;
    } else if (tmp >= 5 && tmp + s.top() != 9) {
      ans++;
      s.pop();
    }
  }
  if (s.size())
    puts("Impossible");
  else
    printf("%d\n", ans);
}
