#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int c[5000001],v[5000001],st,dr;
long long s;
int main()
{
    int n,k,i;
    in>>n>>k;
    v[0]=-10000001;
    for(i=1; i<=n; i++)
    {
        in>>v[i];
        if(i<k)
        {
            while(st<=dr && v[i]<v[c[dr]])
                dr--;
            c[++dr]=i;
        }
        else
        {
            if(i-k>=c[st])
                st++;
            while(st<=dr && v[i]<v[c[dr]])
                dr--;
            c[++dr]=i;
            s+=v[c[st]];
        }

    }
    out<<s;
    return 0;
}