#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],n,k,i,d[5000001],p,u;
long long s;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    p=1;
    u=1;
    for(i=1;i<=n;i++)
    {
        while(p<=u && v[i]<v[d[u]])
        u--;
        d[++u]=i;
        if(i-k==d[p])p++;
        if(i>=k)s+=v[d[p]];


    }
    fout<<s;
    return 0;
}