#include <bits/stdc++.h>

using namespace std;

int v[5000004];


int main() {

    #ifndef ONLINE_JUDGE
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    #endif
    int n,k;
    deque<int> d;
    long long s;
    cin>>n>>k;

    for(int i=1;i<=n;i++)
        cin>>v[i];

    for(int i=1;i<=k;i++)
    {
        if(!d.empty())
        {
            while(!d.empty() && v[d.back()] >= v[i])
                d.pop_back();
        } 
        d.push_back(i);
    }

    s=v[d.front()];
    for(int i=k+1;i<=n;i++)
        {
            while(!d.empty() && v[d.back()] >= v[i])
                d.pop_back();
            d.push_back(i);

            if(i-d.front()>=k)
                d.pop_front();
            s+=v[d.front()];
        }
    cout<<s;
}