#include <fstream>
using namespace std;
ifstream  fin("deque.in");
ofstream fout("deque.out");
int N,K,i,j,A[5000002],DEQUE[5000002],st,dr,vmin;
long long s;
int main()
{
    fin>>N>>K;

    for(i=1; i<=N; i++)
    {
        fin>>A[i];
    }

    s=0;
    st=1;
    dr=0;

    for(i=1; i<=N; i++)
    {
        while(st<=dr && A[i]<=A[DEQUE[dr]])
        {
            dr--;
        }
        dr++;
        DEQUE[dr]=i;

        if(DEQUE[st]==i-K)
        {
            st++;
        }

        if(i>=K)
        {
            s+=A[DEQUE[st]];
        }
    }

    fout<< s;

    return 0;
}