#include <fstream>
#include<bits/stdc++.h>
using namespace std;
deque<pair<int,int> > c;
pair<int,int> aux;
int n,k,x;long long s;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(int i=1;i<=n;++i)
        {
            f>>x;
            aux.first=x;
            aux.second=i;
            while(!c.empty() && c.back().first>=x)
                c.pop_back();
            c.push_back(aux);
            if(i-k==c.front().second) c.pop_front();
            if(i>=k)  s+=c.front().first;
        }
    g<<s<<'\n';
    return 0;
}