#include<fstream>
#define NMAX 5000010
using namespace std;
int V[NMAX], Deque[NMAX], P,U,N,K;
long long S;
int main()
{
    ifstream f("Deque.in");
    ofstream g("Deque.out");
    int i;
    f>>N>>K;
    for(i=1;i<=N;i++)
    f>>V[i];
    P=1;U=0;
    for(i=1;i<=N;i++)
    {
                     while((P<=U)&& V[i]<=V[Deque[U]])
                     U--;
                     Deque[++U]=i;
                     if(Deque[P]==i-K) P++;
                     if(i>=K) 
                     S+=V[Deque[P]];
                     }
                     g<<S;
                     return 0;
                     }