#include <fstream>
#include <utility>
#include <deque>
using namespace std;

typedef pair<int,int> PII;


int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");

    int n,k;
    fin>>n>>k;

    deque<PII> dq;
    long long sum=0;


    for(int i=0;i<n;++i){
        int x;
        fin>>x;

        while(!dq.empty() && dq.front().second <= i-k)
            dq.pop_front();

        while(!dq.empty() && dq.back().first >= x)
            dq.pop_back();

        dq.push_back(PII(x,i));

        if(i+1>=k)
            sum+=dq.front().first;
    }

    fout<<sum<<'\n';
}