#include<fstream>
using namespace std;
int x[5000002],v[5000002];
long long int s=0;
main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int i,j=1,n,stop=0,k;
    f>>n>>k;

    for(i=1; i<k; ++i)
    {
        f>>x[i];

        while(j<=stop && x[i]<=x[v[stop]])
            --stop;

        v[++stop]=i;
    }

    for(i=k;i<=n;i++)
    {
        f>>x[i];

        if(v[j]==i-k)
            j++;

        while(j<=stop && x[i]<=x[v[stop]])
            --stop;

        v[++stop]=i;

        s+=x[v[j]];
    }

    g<<s;
}