#include <iostream>
#include <fstream>
#include <deque>

#define DIM 5000000
using namespace std;

//ifstream f("in.in");
//ofstream g("out.out");

ifstream f("deque.in");
ofstream g("deque.out");


int v[DIM+5],n,k;
deque<int> q;

long long sol = 0;

int main()
{

    f>>n>>k;
    for(int i=1;i<=n;i++){
        f>>v[i];

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

        while(!q.empty() && v[q.back()]>v[i]){
            q.pop_back();
        }

        q.push_back(i);

        if(i>=k){
            sol+=v[q.front()];
        }
    }
    g<<sol;

    return 0;
}