#include<bits/stdc++.h>
using namespace std;
int n,c[27],p;
long long ans;
char a[8001],l; 
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		cin>>a[i];
		c[a[i]-'a'+1]++;
	}
	for(int i=1;i<27;i++)
		if(c[i]%2)l=i+'a'-1,p++;
	if(p>1&&p%2){
		printf("Impossible");
		return 0;
	}
	if(a[1]==l){
		ans++;
		swap(a[1],a[2]);
	}
	for(int i=1;i<=n/2;i++){
		for(int j=n-i+1;j>i;j--){
			if(a[j]==a[i]){
				ans+=n-i+1-j;
				for(int k=j;k<=n-i+1;k++){
					swap(a[k],a[k+1]);
					
				}
			}
		}
	}
	printf("%lld",ans);
	return 0;
}
/**************************************************************
	Problem: 1842
	User: chenshuo
	Language: C++
	Result: Time Limit Exceed
****************************************************************/