#include <iostream>
#include<fstream>


using namespace std;

const long long N =5000001;
ifstream in("deque.in");
ofstream out("deque.out");

int d[N],v[N];
long long sum;

int main()
{
    int n,k,i,st=0,dr=-1;
    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)
            sum+=v[d[st]];
    }
    out<<sum;
    return 0;
}