#include <iostream>
#include <fstream>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
const int N=5000000;
int v[N], d[N];
int main()
{
    int n,k, i, st=0, dr=-1;
    long long s=0;
    in>>n>>k;
    for(i=0; i<n; i++)
    {
        in>>v[i];
        if (st<=dr && d[st]==i-k)
            st++;
        while(st<=dr && v[i]<= v[d[dr]])
            dr--;
        d[++dr]=i;
        if(i>=k-1)
            s+=v[d[st]];
    }

    out<<s;
    return 0;
}