#include<iostream>
#include<algorithm>
using namespace std;
long long n,k,maxn,sum,ans;
char ch;
struct CF462B{
    char c;
    long long sl;
}a[100010];
long long cmp(CF462B x,CF462B y){
    return x.sl>y.sl;
}
int main()
{
    cin >> n >> k;
    for(long long i=1;i<=n;i++){
        cin >> ch;
        a[ch-'A'+1].sl++;
        a[ch-'A'+1].c=ch;
        maxn=max((long long)(ch-'A'+1),maxn);
    }
    sort(a+1,a+maxn+1,cmp);
    for(long long i=1;i<=maxn;i++){
        for(long long j=1;j<=a[i].sl;j++){
            if(k!=0)sum++;
            else break;
            k--;
        }
        ans+=sum*sum;
        if(k==0)break;
        else sum=0;
    }
    cout << ans << endl;
    return 0;
}