#include <bits/stdc++.h>

using namespace std;
ifstream  fin("deque.in");
ofstream fout("deque.out");
int i,n,k,p,u,v[5000005],m[5000005];
long long s;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)fin>>v[i];
    m[1]=1;
    p=u=1;
    for(i=2;i<=n;i++)
    {
        while(p<=u&&v[i]<=v[m[u]])u--;
        u++;
        m[u]=i;
        if(i-m[p]==k)p++;
        if(i>=k)s+=v[m[p]];
    }
    fout<<s;
    return 0;
}