#include <iostream>
#include <fstream>
using namespace std;
int v[5000000], d[5000000];
int main()
{
    int f = 1, r = 0, n, k;
    long long s = 0;
    ifstream fin("deque.in");
    ifstream fout("deque.out");
    fin>>n>>k;
    for(int i = 1; i <= n; i++)
        fin>>v[i];
    for(int i = 1; i <= n; i++){
        while(f <= r && v[i] <= v[d[r]])
            r--;
        d[++r] = i;
        if(d[f] == i-k)
            f++;
        if(i >= k)
            s = s+v[d[f]];
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}