#include <iostream>
#include <fstream>

using namespace std;

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

const int N = 5000001;
int v[N],d[N];
int main()
{
    int i,st,dr,n,k;
    long long sum = 0;
    in>> n >> k;
    st = 0;
    dr = -1;
    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){
            sum += v[d[st]];
        }
    }
    out << sum;
    return 0;
}