#include <bits/stdc++.h>
using namespace std;
const double pi = 4.0 * atan(1.0);
const int N = 10000000;
char *str;
stack<int> stc;
int convert(char ch) {
  switch (ch) {
    case '<':
      return 1;
    case '(':
      return 2;
    case '[':
      return 3;
    case '{':
      return 4;
    case '>':
      return 5;
    case ')':
      return 6;
    case ']':
      return 7;
    case '}':
      return 8;
  }
}
void init() { str = (char *)malloc(N * sizeof(char)); }
int main() {
  int T, cnt, flag, tmp, changes;
  flag = 1;
  changes = 0;
  init();
  scanf("%s", str);
  cnt = 0;
  while (str[cnt] != '\0') {
    tmp = convert(str[cnt]);
    if (tmp <= 4)
      stc.push(tmp);
    else {
      if (stc.size() == 0) {
        flag = 0;
        break;
      }
      if (stc.top() >= 5) {
        flag = 0;
        break;
      } else if (tmp - 4 == stc.top())
        stc.pop();
      else if (tmp - 4 != stc.top()) {
        stc.pop();
        changes++;
      }
    }
    cnt++;
  }
  if (!flag || stc.size() != 0)
    printf("Impossible\n");
  else
    printf("%d\n", changes);
}
