#include <bits/stdc++.h>
using namespace std;

#ifdef LOCAL
ifstream fin("file.in");
ofstream fout("file.out");
#else // LOCAL
ifstream fin("deque.in");
ofstream fout("deque.out");
//#define fin cin
//#define fout cout
#endif // LOCAL
//#define int long long
#pragma GCC optimize("O2")

int c,n,m,t,k;
long long sum;
deque<int>dq;
int v[5000005];

void put(int it)
{

}

signed main()//97-122
{
    fin>>n>>k;
    for(int i=1;i<=n;++i)fin>>v[i];
    for(int i=1;i<=n;++i)
    {
        while(!dq.empty()&&v[dq.back()]>=v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);

        if(i<k)continue;
        while(dq.front()<=i-k)dq.pop_front();
        sum+=v[dq.front()];
    }
    fout<<sum;


    return 0;
}