#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k, i;
int v[5000005];
long long sum=0;
deque<int> dq;

int main()
{
    fin>>n>>k;

    for(i=1;i<=n;i++){
        fin>>v[i];
    }

    for(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(i=k+1;i<=n;i++){
        while(!dq.empty() && v[dq.back()]>v[i]){
            dq.pop_back();
        }

        while(!dq.empty() && dq.front()<i-k+1){
            dq.pop_front();
        }

        dq.push_back(i);

        sum+=v[dq.front()];
    }

    fout<<sum;



    return 0;
}