#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long N,K,i,v[5000010],s;
deque <long long> d;
int main()
{
    fin>>N>>K;
    for(i=1;i<=N;i++)
    {
        fin>>v[i];
    }
    for(i=1;i<=K;i++)
    {
        while(!d.empty()&&d.back()>v[i])
            d.pop_back();
        d.push_back(v[i]);
    }
    s=d.front();
    for(i=K+1;i<=N+1;i++)
    {
        while(!d.empty()&&d.back()>v[i])
            d.pop_back();
        d.push_back(v[i]);
        if(d.front()==v[i-K])
            d.pop_front();
        s=s+d.front();
    }
    fout<<s;
}