#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int deque[5000003],n,k,a[5000003],Begin,End;
long long sum;
void read()
{
    f>>n>>k;
    int i;
    for(i=1;i<=n;i++)
        f>>a[i];
}
void calculate()
{
    int i;
    Begin=1;End=0;
    for(i=1;i<=k;i++)
        {
            while(Begin<=End&&a[i]<=a[deque[End]])
                End--;
            deque[++End]=i;
        }
    sum=a[deque[Begin]];
    for(i=k+1;i<=n;i++)
    {
        while(Begin<=End&&a[i]<=a[deque[End]])
                End--;
            deque[++End]=i;
        if(deque[Begin]==i-k) Begin++;
    sum+=a[deque[Begin]];
    }
}
void print()
{
    g<<sum<<"\n";
}
int main()
{
    read();
    calculate();
    print();
    return 0;
}