#include <bits/stdc++.h>
using namespace std;
const int maxn = 1000000 + 10;
char a[maxn];
int top, s[maxn];
int id(char c) {
  if (c == '(') return 0;
  if (c == ')') return 1;
  if (c == '[') return 2;
  if (c == ']') return 3;
  if (c == '{') return 4;
  if (c == '}') return 5;
  if (c == '<') return 6;
  if (c == '>') return 7;
}
int main() {
  scanf("%s", a);
  top = 0;
  int ans = 0;
  for (int i = 0; a[i]; i++) {
    int t = id(a[i]);
    if (!(t & 1)) {
      s[top++] = i;
    } else {
      if (top == 0) {
        printf("Impossible\n");
        return 0;
      }
      top--;
      if ((t ^ id(a[s[top]])) != 1) ans++;
    }
  }
  if (top)
    printf("Impossible\n");
  else
    printf("%d\n", ans);
  return 0;
}
