#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

long long n, k, st, dr=-1, sol;

int main()
{
    fin>>n>>k;
    vector<long long> v(n);
    vector<long long> poz(n);

    for(long long i = 0; i < n; i++)
    {
        fin>>v[i];
        while(st<=dr && v[i]<=v[poz[dr]]) dr--;
        dr++;
        poz[dr]=i;
        if(poz[st]==poz[dr]-k)
            st++;
        if(poz[dr]+1>=k)
            sol+=v[poz[st]];
    }

    fout<<sol;

    return 0;
}