#include <fstream>
#define Nmax 5000010
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,j,st=1,dr,D[Nmax],A[Nmax];
long long sum;
int main()
{   f>>n>>k;
    for(int i=1;i<=n;i++) f>>A[i];
    for(int i=1;i<=n;i++)
    {   while(st<=dr and A[i]< A[D[dr]]) dr--;
        D[++dr]=i;
        if(D[st]<=i-k) st++;
        if(i>=k) sum+=A[D[st]];
    }
    g<<sum<<'\n'; g.close(); return 0;
}