#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,fr,b,v[5000002],Q[5000002],j,i;
long long s;
int main()
{
    f>>n>>k;
    for(i=1; i<=n; i++)
    {
        f>>v[i];
    }
    fr=1;
    b=0;
    for(i=1; i<=n; i++)
    {
        while(fr<=b&&v[i]<=v[Q[b]])b--;
        Q[++b]=i;
        if(Q[fr]==i-k)fr++;
        if(i>=k)s+=v[Q[fr]];
    }
    g<<s;

    return 0;
}