#include <cstdio>  
#include <cstdlib>  
  
int main()  
{  
#ifdef LOCAL  
    freopen("input2.txt", "r", stdin);  
#endif  
    int n, flag = 0, ans = 0;  
    char *str;  
    scanf("%d", &n);  
    str = (char*)malloc(n * sizeof(char));  
    scanf("%s", str);  
    int j = n - 1, p = 0;  
    for(int i = 0; i < j; i++)  
    {  
        for(int k = j; k >= 0; k--)  
        {  
            if(k == i)  
            {  
                flag++;  
                if(n % 2 == 0 || flag > 1)  
                {  
                    printf("Impossible\n");  
                    return 0;  
                }  
                p = n/2 - i;  
                break;  
            }  
            else if(str[k] == str[i])  
            {  
                ans += j - k;  
            //  printf("ans = %d\n", ans);  
                for(int f = k; f < j; f++)  
                {  
                    str[f] = str[f + 1];  
                }  
                str[j] = str[i];  
                j--;  
                break;  
            }   
        }  
    }  
    printf("%d\n", ans + p);  
    return 0;  
}