#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const int NMAX=5000005;
deque<int>Q;
int n,k,a[NMAX];
long long sol;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=k;i++)
    {
        int x;
        fin>>a[i];
        x=a[i];
        while(!Q.empty() && a[Q.back()]>=x)
            Q.pop_back();
        Q.push_back(i);
    }
    sol+=(a[Q.front()]);
    for(int i=k+1;i<=n;i++)
    {
        int x;
        fin>>a[i];
        x=a[i];
        while(!Q.empty() && a[Q.back()]>=x)
            Q.pop_back();
        Q.push_back(i);
        if(i-Q.front()>=k)
            Q.pop_front();
        sol+=a[Q.front()];
    }
    fout<<sol<<"\n";
    fin.close();
    fout.close();
    return 0;
}