import java.io.*;

import java.util.*;

public class Main {

static final Reader in = new Reader();

public static void main(String[] args) {

int n=in.nextInt();

long x=in.nextInt(), ans=Long.MAX_VALUE;

long[] ps = new long[n+1];

for(int i=0; i<n; ++i)

ps[i+1]=ps[i]+in.nextInt();

for(int i=1; i<=n; ++i) {

long ca=2*(ps[n]-ps[n-i])+i*x;

for(int j=0; n-i*j>0; ++j) {

long b=(2*j+3)*(ps[n-i*j]-ps[Math.max(n-i*(j+1), 0)]);

if(Long.MAX_VALUE-b<ca) {

ca=Long.MAX_VALUE;

break;

}

}

ans=Math.min(ca, ans);

}

System.out.println(ans+n*x);

}

static class Reader {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

StringTokenizer st;

String next() {

while(st==null||!st.hasMoreTokens()) {

try {

st = new StringTokenizer(br.readLine());

} catch(Exception e) {}

}

return st.nextToken();

}

int nextInt() {

return Integer.parseInt(next());

}

}

}