#include<bits/stdc++.h>
using namespace std;
ifstream fin ("deque.in");
ofstream fout("deque.out");
int v[5000002],dq[5000000];


int main ()
{
    long long ans=0;
    int n,i,k,st=1,dr=0;
    fin>>n>>k;
    ///LUCRAM PE POZITII NU PE NUMERE
    for (i=1;i<=n;i++)
    {
        fin>>v[i];
        if (i-k==dq[st])
            ++st;
        while (st<=dr && v[dq[dr]]>v[i])
            --dr;
        dq[++dr]=i;
        if (i>=k)
            ans=ans+v[dq[st]];
    }
    fout<<ans<<'\n';
    return 0;
}