#include <fstream>
#include <iostream>

#define N_MAX 5000005


using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int v[N_MAX], init[N_MAX];

int main() {
    unsigned int ii, i, j, n, k;
    long long sum = 0;

    fin >> n >> k;
    for(ii = 1; ii <= n; ++ii)
        fin >> init[ii];

    for(ii = 1, j = 0, i = 1; ii <= n; ++ii){
        while(i <= j && j >= 0 && init[ii] <= init[v[j]])
            --j;

        v[j + 1] = ii;
        ++j;

        if(v[i] == ii - k)
            ++i;

        if(ii >= k)
            sum += init[v[i]];
    }

    fout << sum;

    return 0;
}