#include <bits/stdc++.h>
#define val first
#define poz second
#define ll long long
#define pii pair<int,int>
#define pb push_back
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int n,k;
ll sum;

deque <pii> dq;

void Read();
void Solve();

int main()
{   Read();
    Solve();
    f.close();
    g.close();
}

void Read()
{   f>>n>>k;
    for(int nr,i=1; i<=k; i++)
    {   f>>nr;
        if(!dq.empty())
        {   while(nr<dq.back().val)
            {   dq.pop_back();
                if(dq.empty())
                    break;
            }
        }
        dq.pb({nr,i});
    }
    sum=dq.front().val;
}

void Solve()
{   for(int nr,i=4; i<=n; i++)
    {   if(dq.front().poz<i-k+1)
            dq.pop_front();
        f>>nr;
        if(!dq.empty())
        {   while(nr<dq.back().val)
            {   dq.pop_back();
                if(dq.empty())
                    break;
            }
        }
        dq.pb({nr,i});
        sum=1LL*(sum+dq.front().val);
    }
    g<<sum;
}