#include<bits/stdc++.h>
using namespace std;
int main()
{
int n,cnt=0,sum=0,m=0;
cin>>n;
string s;
cin>>s;
int left=0,right=n-1;
while(left<right)
{
int l=left,r=right;
while(s[l]!=s[r]&&l<=r)r--;
if(lr)
{
sum++;
if(n%20)
{
cout<<"Impossible";
return 0;
}
else
{
if(sum>1)
{
cout<<"Impossible";
}
m=l;
right++;
}
}
else if(r!=right)
{
for(int i=r;i<right;i++)
{
swap(s[i],s[i+1]);
cnt++;
}
}
left++;
right--;
}
if(m)cout<<cnt+n/2-m;
else cout<<cnt;
return 0;
}
