#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int a[50000000],dek[50000000],k,n;
long long suma;

int main()
{   in>>n>>k;
    int i,prim=1,ultim=0;
    for(i=1; i<=n; i++)
        in>>a[i];
    for(i=1; i<=n; i++)
        {while(a[i]<=a[dek[ultim]] && prim<=ultim)
            ultim--;
        ultim++;
        dek[ultim]=i;
        if(dek[prim]<=i-k)
            prim++;
        if(i>=k)
            suma+=a[dek[prim]];}
out<<suma;
in.close();
out.close();

    return 0;
}