#include <fstream>
#define maxi 5000005
using namespace std;

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

int n, k, x, prim=1, ultim=0;
int coada[maxi], v[maxi];
long long suma;

int main()
{
    in>>n>>k;

    for(int i=1; i<=n; i++)
        in>>v[i];

    for(int i=1; i<=n; i++)
    {
        while(prim<=ultim && v[i]<=v[coada[ultim]])
            ultim--;
        coada[++ultim]=i;

        if(coada[prim]==i-k)
            prim++;

        if(i>=k)
            suma+=v[coada[prim]];
    }

    out<<suma;

    in.close();
    out.close();
    return 0;
}