#include <iostream>
#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int v[5000000], d[5000000];

int main()
{
    int n, k, i, st, dr;
    long long s = 0;
    f >> n >> k;
    dr = -1;
    for ( i = st = 0; i < n; i++ ) {
        f >> v[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]];
        }
    }
    g << s;
    f.close();
    g.close();
    return 0;
}