#include <fstream>

using namespace std;

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

#define N 5000005
int n, k, a[N];
long long s;
int Q[N], prim, ultim;
int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> a[i];
    prim = 1;
    ultim = 0;
    for(int i = 1; i <= n; i++)
    {
        while(prim <= ultim && a[i] <= a[Q[ultim]])
            ultim--;
        Q[++ultim] = i;
        if(Q[prim] == i - k)
            prim++;
        if(i >= k)
            s += a[Q[prim]];
    }
    fout << s;
    return 0;
}