#include <bits/stdc++.h>

using namespace std;
int v[5000002],k,n;
long long int sum;
ifstream f("deque.in");
ofstream g("deque.out");
deque < int > dq;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; ++i)
        f>>v[i];
    for (int i=1; i<=k; ++i)
    {
        while(!dq.empty() && v[dq.back()]>=v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }
    sum = v[dq.front()];
    for (int i=k+1; i<=n; ++i)
    {
        while(!dq.empty() && v[dq.back()]>=v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front()<i-k+1)
            dq.pop_front();
        sum+=v[dq.front()];
    }
    g<<sum;
    return 0;
}