#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long st,dr,i,n,k,v[5000001],dq[5000001],sum;
int main()
{
    st=0;
    dr=-1;
    fin>>n>>k;
    for(i=1; i<=n; ++i)
    {
        fin>>v[i];
        if(st<=dr&&dq[st]==i-k)
            st++;
        while(st<=dr&&v[i]<=v[dq[dr]])
            dr--;
        dq[++dr]=i;
        if(i>=k)
            sum+=v[dq[st]];
    }
    fout<<sum;
}