#include <fstream>
#define MAX_N 5000000

using namespace std;

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

int v[MAX_N], d[MAX_N];

int main()
{
    ios_base::sync_with_stdio(false);
    int n, k, st, dr;
    long long s = 0;
    fin >> n >> k;

    for(int i = 0 ; i < n ; i++)
        fin >> v[i];


    st = 0;
    dr = -1;
    for(int i = 0 ; i < n ; i++){
        if(st <= dr && d[st] == i - k)
            st++;
        while(st <= dr && v[i] <= v[d[dr]])
            dr--;
        d[++dr] = i;
        if(i >= k - 1)
            s += v[d[st]];
    }

    fout << s;
    return 0;
}