#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long N,K,i,A[5000005],s;
struct val
{
    long long val, poz;
};
deque <val> Q;
val x;
int main()
{
    fin>>N>>K;
    for(i=1;i<=N;i++)
        fin>>A[i];
    for(i=1;i<=K;i++)
    {
        while(!Q.empty() && Q.back().val>A[i])
        {
            Q.pop_back();
        }
        x.val=A[i];
        x.poz=i;
        Q.push_back(x);
    }
    for(i=K+1;i<=N;i++)
    {
        s+=Q.front().val;
        while(!Q.empty() && Q.back().val>A[i])
        {
            Q.pop_back();
        }
        while(!Q.empty() && Q.front().poz<=i-K)
        {
            Q.pop_front();
        }
        x.val=A[i];
        x.poz=i;
        Q.push_back(x);
    }
    s+=Q.front().val;
    fout<<s;
    return 0;
}