#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

long long p,u,s,i,j,m,n,k;
int t[5000003],q[5000003];
int main()
{
    fin>>n>>k; p=1;u=0;
    for (i=1;i<=n;i++)
    {
        fin>>t[i];
        while (p<=u && t[q[u]]>=t[i]) u--;
        u++;
        q[u]=i;
        if (q[p]==i-k) p++;
        if (i>=k)
            s+=t[q[p]];
    }
    fout<<s;
    return 0;
}