#include<bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>>dq;
int n,k;
int v[5000001];
long long sum;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    dq.push_back({v[1],1});
    for(int i = 2; i <= k; ++i)
    {
        while(!dq.empty() && v[i] <= dq.back().first)
            dq.pop_back();
        dq.push_back({v[i],i});
    }
    sum = dq.front().first;
    for(int i = k+1; i <= n; ++i)
    {
        while(!dq.empty() && v[i] <= dq.back().first)
            dq.pop_back();
        dq.push_back({v[i],i});
        if(dq.front().second == i - k)
            dq.pop_front();
        sum += dq.front().first;
    }
    g<<sum;
}