#include <iostream>
#include <fstream>

using namespace std;

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

const int N=500001;

int main()
{
    int n,k,r=0,st=0,dr=-1;
    long long a[N],d[N];
    in>>n>>k;
    for(int i=0;i<n;i++)
    {
        in>>a[i];
        if(st<=dr&&d[st]==i-k)
        {
            st++;
        }
        while(st<=dr&&a[i]<=a[d[dr]])
        {
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1)
        {
            r+=a[d[st]];
        }
    }
    out<<r;
    return 0;
}