#include <fstream>
#define Nmax 500010

using namespace std;

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

int n,k;
int v[Nmax],Deque[Nmax];

int main()
{
    in>>n>>k;
    int top=0,bottom=0;
    long long sum=0;
    for(int i=1;i<=n;i++) in>>v[i];

    for(int i=1;i<=n;i++)
    {
        in>>v[i];
        while(top> bottom && v[i] < v[Deque[top-1]]) top --;
        Deque[top++]=i;
        if(Deque[bottom]==i-k) bottom++;
        if(i>=k) sum+=v[Deque[bottom]];
    }

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