#include <iostream>
#include <fstream>
#include <bits/stdc++.h>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
long long n,k,fr=0,bk=-1,i,sum;
int main() {
    f >> n >> k;
    int d[n+1], v[n+1];
    
    while(i<n)
    {
        f>>v[i];
        while(fr<=bk && v[d[bk]]>v[i]){
            bk--;
        }
        bk++;
        d[bk]=i;
        if(d[fr]==i-k){
            fr++;
        }
        if(i>=k-1){
            sum+=v[d[fr]];
        }
        i++;
    }
    g<<sum;
    f.close();
    g.close();

    return 0;
}