#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,x,s,minn,v[5000001];
set <int> se;

int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
    {
        f>>v[i];
        if(i<=k)
            se.insert(v[i]);
    }
    s+=*se.begin();
    for(int i=k+1;i<=n;i++)
    {
        se.erase(v[i-k]);
        se.insert(v[i]);
        s+=*se.begin();
    }
    g<<s;
    return 0;
}