#include<bits/stdc++.h>
#define MAX_CHAR 26
using namespace std;
string S;
int k;
int PoWMod(int n){
int tong = 1;
for(int i = 1; i <= 2; i++){
tong *= n;
}
return tong;
}
void Min_String(){
cin>>k;
cin.ignore();
getline(cin,S);
int F[MAX_CHAR];
memset(F, 0, sizeof(F));
for(int i=0;i < (int)S.size();i++){
F[S[i]-'a']++;
}
priority_queue<int> Q;
for(int i=0;i<MAX_CHAR;i++){
Q.push(F[i]);
}
while(k--){
int t=Q.top();
Q.pop();
t--;
Q.push(t);
}
long long tong = 0;
while(!Q.empty()){
int s=Q.top();
tong += (1ll)*PoWMod(s);
Q.pop();
}
cout << tong;
}
int main(){
Min_String();
}