#include <iostream>
#include <fstream>
#include <deque>
#include <vector>
using namespace std;
deque <int> deque1,deque2;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n,k,nr,i,x;
    long long sum=0;
    fin>>n>>k;
    for(i=1;i<=k;i++)
    {
        fin>>x;
        if(!deque1.empty())
        {
            while(!deque1.empty()&&deque1.back()>=x)
            {
                deque1.pop_back();
                deque2.pop_back();
            }
        }
        deque1.push_back(x);
        deque2.push_back(i);
    }
    sum+=deque1.front();
    for(i=k+1;i<=n;i++)
    {
        fin>>x;
        if(!deque1.empty())
        {
            while(!deque1.empty()&&deque1.back()>=x)
            {
                deque1.pop_back();
                deque2.pop_back();
            }
        }
        deque1.push_back(x);
        deque2.push_back(i);
        if(deque2.front()<i-k+1){
            deque2.pop_front();
            deque1.pop_front();
        }
        sum+=deque1.front();
    }
    fout<<sum;
    return 0;
}