#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int Nmax=5000005;
long long  v[Nmax],deq[Nmax];
int main()
{long long n,k,s=0;
f>>n>>k;
for(int i=1;i<=n;i++)
    f>>v[i];
int fro=1,bac=0;
for(int i=1;i<=n;i++)
{
    while(fro<=bac && v[i]<=v[deq[bac]])
        bac--;
    deq[++bac]=i;
    if(i-k==deq[fro])
        fro++;
    if(i>=k)
        s+=v[deq[fro]];
}

g<<s;
    return 0;
}