#include <fstream>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

long long d[5000000], n, v[500000], p=1, q, k, s;

int main()
{
    in>>n>>k;
    for(int i = 0; i<n; i++)
    {
        in>>v[i];
        while(v[d[q]]>=v[i] && q>=p)
            q--;

        d[++q] = i;

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

        if(i>=k-1)
        s+=v[d[p]];
    }

    out<<s<<'\n';
    return 0;
}