#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int n, k;
struct Func{
int p;
double q;
Func(){}
Func(int _p, double _q): p(_p), q(_q) {}
double operator()(int x) const{
return pow(x-p, (double)k/2) + q;
}
};
int cross(const Func &f, const Func &g){
int l = g.p + 1, r = n, ans = n+1;
while(l<=r){
int mid = (l+r)>>1;
if (f(mid) >= g(mid)) ans = mid, r = mid-1;
else l = mid+1;
}
return ans;
}
struct Hull{
vector<Func> st;
vector<double> C;
void insert(Func g){
// printf("insert %d %f\n", g.p, g.q);
double tmp = 0;
while(st.size() >= 2){
tmp = cross(st.back(), g);
if (C.back() > tmp) break;
st.pop_back();
C.pop_back();
}
if (st.size() >= 2) C.push_back(tmp);
else if (st.size() == 1) C.push_back(cross(st.back(), g));
st.push_back(g);
}
double query(int x){
int l = 0, r = (int)st.size()-2, ans = (int)st.size()-1;
while(l<=r){
int mid = (l+r)>>1;
if (x >= C[mid]) ans = mid, r = mid-1;
else l = mid+1;
}
// for (int i=0;i<(int)st.size();i++) printf("%f ", st[i](x));
// printf("\n");
// printf("return: %f \n", st[ans](x));
return st[ans](x);
}
}H[1001000];
int a[1001000], idx[1001000], cnt[1001000];
double dp[1001000];
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> k >> n;
for (int i=1;i<=n;i++){
cin >> a[i];
cnt[a[i]]++;
idx[i] = cnt[a[i]];
}
if (k==2){
printf("%.15f\n", (double)n);
return 0;
}
for (int i=1;i<=n;i++){
// printf(" ok %d %f\n", idx[i]-1, dp[i-1]);
H[a[i]].insert(Func(idx[i]-1, dp[i-1]));
dp[i] = H[a[i]].query(idx[i]);
// printf("%d -> %.15f\n", i, dp[i]);
}
printf("%.15f\n", dp[n]);
}
