#include <iostream>
#include <fstream>
#include <algorithm>
#include <bitset>

using namespace std;
ifstream fin ("deque.in");
ofstream fout("deque.out");
int v[5000005],p,u,d[5000005],i,k,n;
long long s;

int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    p=1;
    u=1;
    d[p]=1;
    for(i=2;i<=n;i++)
    {
        while(p<=u&&v[i]<=v[d[u]])
            u--;
        u++;
        d[u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}