#include <iostream>
#include <fstream>
#define N 5000010
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int n, k, A[N], d[N], a1=1, a2;
long long S;

int main()
{
    f >> n >> k;
    for(int i=1; i<=n; i++)
        f >> A[i];
    int i = 1;
    while(i <= n)
    {
        while (A[i] <= A[d[a2]] && a1 <= a2)
            a2--;
        d[++a2] = i;
        if (d[a1]==i-k)
            ++a1;
        if(i>=k)
            S+=A[d[a1]];
        ++i;
    }
    g << S;

    return 0;

}