#include <iostream>
#include <fstream>

using namespace std;

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

int v[5000001], w[5000001], N, K;
long long s;

int main()
{
    int i, sf, in;
    f>>N>>K;
    for(i=1; i<=N; i++)
        f>>v[i];
    sf=0;
    in=1;
    for(i=1; i<=N; i++)
    {
        while(in<=sf && v[i]<=v[w[sf]])
            sf--;
        w[++sf]=i;
        if(w[in] == i-K)
            in++;
        if(i>=K)
            s=s+v[w[in]];
    }
    g<<s;
    return 0;
}