/*******************************\
   Name:    REAJUL HAQUE REAYZ  |
   School:  COMILLA UNIVERSITY  |
            CSE (5TH BATCH)     |
********************************/
#include<bits/stdc++.h>
#define endl "\n"
#define linf 100000000000000000
#define pi acos(-1.0)
#define pb push_back
#define mp make_pair
#define ss stringstream
#define ll long long int
#define all(v) v.begin(), v.end()
#define mem(x,y) memset(x,y,sizeof(x))
#define bit_cnt(mask) __builtin_popcount(mask)
using namespace std;
#define MOD 1000000007
ll bigmod(ll n, ll r)
{
    if(r==0) return 1;
    if(r==1) return n;
    if(r%2==0)
    {
        ll ret = bigmod(n, r/2);
        return ((ret%MOD) * (ret%MOD)) % MOD;
    }
    else return ((n%MOD) * (bigmod(n,r-1)%MOD)) % MOD;
}
ll modinverse(ll a){return bigmod(a,MOD-2)%MOD;}
ll lcm(ll a, ll b) {a=abs(a); b=abs(b); return (a/__gcd(a,b))*b;}
ll gcd(ll a, ll b) {a=abs(a); b=abs(b); if(!b) return a; return __gcd(b,a%b);}
#define MAX 100005

int n, k, c[10004], dp[10004];
int main()
{
    cin>>n>>k;
    for(int i=0; i<n; i++) cin>>c[i];
    ll cost=0, mn=linf;
    int i=0;
    while(i<n){
        if(i+k<n){
            i += k;
            cost += c[i];
            i += k;
            i++;
            continue;
        }
        int temp=1000000009;
        for(; i<n; i++) temp=min(temp,c[i]);
        cost += temp;
    }
    cout<<cost<<endl;
    return 0;
}