#include <fstream>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001], d[5000001];
long long p=0, l=0, minim, n, k, i, sum;
int main()
{
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>v[i];

    for(i=1; i<=n; i++)
    {
        while(p<=l && v[i]<v[d[l]])l--;
            d[++l]=i;
            if(i-k==d[p])
                p++;

            if(i>=k)
                sum+=v[d[p]]
                ;


    }

    fout<<sum;
    return 0;
}