#include <fstream>
#define NMAX 5000001

using namespace std;

fstream fin("deque.in", ios::in);
fstream fout("deque.out", ios::out);

int n,k,i,a,b;
int v[NMAX],p[NMAX];
long long s;

int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    fin>>v[i];
    b=0;a=1;
        for(i=1;i<=n;i++) {
            while(a<=b && v[i]<=v[p[b]])
                b--;
            p[++b]=i;
            if(p[a]==i-k) a++;
            if(i>=k)s+=v[p[a]];
        }
    fout<<s;
    return 0;
}