#include <iostream>
#include <fstream>
#include <climits>
#include <queue>
#define NMAX 5000045

using namespace std;

fstream fin("deque.in", ios::in);
fstream fout("deque.out", ios::out);
int n,k,x;
int v[NMAX];
long long sum;
deque <int> deq;

int main()
{
    fin>>n>>k;
    int j=1,d;
    int ok;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(d=1; d<=k; d++)
        deq.push_back(v[d]);
    while(j!=n-1) {
        ok=v[j];
        for(int y=1; y<=k; y++) {
            if(ok>deq.front()) ok=deq.front();
            deq.push_back(deq.front());
            deq.pop_front();
        }
        sum+=ok;
        deq.pop_front();
        j++;
        deq.push_back(v[d++]);
    }
    fout<<sum;
    return 0;
}