#include <bits/stdc++.h>
using namespace std;
#define GG ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int main () { GG;
string s;	cin>>s;
int n=s.size(),er=0,openb=0;
vector<int>v(5);
for(int i=0;i<n;i++)
{	if(s[i]=='(')	  v[1]++;
	else if(s[i]=='{') v[2]++;
	else if(s[i]=='[') v[3]++;
	else if(s[i]=='<') v[4]++;

	else if(s[i]==')')
	{	if(v[1]>0) v[1]--;
		else er++;
	}
	else if(s[i]=='}')
	{	if(v[2]>0) v[2]--;
		else er++;
	}
	else if(s[i]==']')
	{	if(v[3]>0) v[3]--;
		else er++;
		
	}
	else if(s[i]=='>')
	{	if(v[4]>0) v[4]--;
		else er++;
	}
}
openb=v[1]+v[2]+v[3]+v[4];

if(openb==er)	 cout<<er<<"\n";
else		 cout<<"Impossible\n";
return 0;}