#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
deque<pair<int,int> > d;
int n,k,i,x;
long long sum;
int main()
{
    f>>n>>k;
    for (i=0;i<n;i++)
    {
        f>>x;
        while(!d.empty()&&d.front().second<=i-k) d.pop_front();
        while(!d.empty()&&d.back().first>=x) d.pop_back();
        d.push_back(make_pair(x,i));
        if(i>k-2) sum+=d.front().first;
    }
    g<<sum;
    return 0;
}