#include <bits/stdc++.h>
using namespace std;
map<char,char>ope{{'<','>'},{'{','}'},{'[',']'},{'(',')'}};
int main(){
string s;
stack<char>stk;
int ans=0;
cin>>s;
for(char c:s){
if(ope.find(c)!=ope.end())stk.push(c);
else{
if(stk.empty()){ans=-1;break;}
else{
if(ope[stk.top()]!=c)ans++;
stk.pop();}
}
}
if(ans==-1||stk.size())cout<<"Impossible\n";
else cout<<ans<<'\n';
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