#include <iostream>
#include <fstream>
using namespace std;
int v[5000001], d[5000001];
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int st=0, dr=-1,i,n,k;
    long long s=0;
    in>>n>>k;
    for(i=0; i<n; i++)
    {
        in>>v[i];
        if(st<=dr && d[st]==i-k)
        {
             st++;
        }
        while(st<=dr && v[i]<=v[d[dr]])
        {
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1)
        {
            s+=v[d[st]];
        }
    }
    out<<s;
    return 0;
}