#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,a;
typedef pair <int,int> P;
int main()
{
    long long s=0;
    fin>>n>>k;
    deque<P> q;
    for(i=1;i<=n;i++)
    {
        fin>>a;
        while(!q.empty() && q.back().first>=a) q.pop_back();
        q.push_back(P(a,i));
        while(q.front().second<=i-k) q.pop_front();
        if(i>=k) s+=q.front().first;
    }
    fout<<s;
}