#include <iostream>
#include <fstream>
#define NMax 5000010
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i;
int a[NMax],Deque[NMax];
int Front,Back;
long long sum;
int main()
{
fin>>n>>k;
for(i=1;i<=n;i++)
    fin>>a[i];
Front=1;
Back=0;
for(i=1;i<=n;i++)
{
    while(Front<=Back&&a[i]<a[Deque[Back]])
        Back--;
    Deque[++Back]=i;
    if(Deque[Front]==i-k) Front++;
    if(i>=k) sum+=a[Deque[Front]];
}
fout<<sum;
    return 0;
}