#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, i, j, k, v[5000005];
long long s;
deque <int> dq;

int main()
{   f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    for(i=1;i<=n;i++)
    {   while(!dq.empty() && v[dq.back()]>=v[i] )
            dq.pop_back();
        dq.push_back(i);
        if(i-k==dq.front())
           dq.pop_front();
        if(i>=k)
        {   s=s+v[dq.front()];
            //cout<<s<<endl;
        }
    }
    g<<s;

    return 0;
}