#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long s,n,x,y,k,v[5000001];
deque <int> d;
int main()
{
    f>>n>>k;
    f>>v[1];
    d.push_back(1);
    for(int i=2;i<=k;i++)
    {
        f>>v[i];
        while(!d.empty() && v[d.back()]>v[i])
            d.pop_back();
        d.push_back(i);
    }
    s=s+v[d[0]];
    for(int i=k+1;i<=n;i++)
    {
        f>>v[i];
        if(d[0]==i-k)
            d.pop_front();
         while(!d.empty() && v[d.back()]>v[i])
            d.pop_back();
        d.push_back(i);
        s=s+v[d[0]];
    }
    g<<s;
    return 0;

}