#include<fstream>
using namespace std;
#define NMAX 5000005
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,p,u,a[NMAX],D[NMAX];
long long s;
int main()
{
    int i;
    fin>>n>>k;
    p=1, u=0;
    for (i=1;i<=n;++i)
    {
        fin>>a[i];
        while (p<=u && a[i]<a[D[u]])
            --u;
        D[++u]=i;
        if (i>=k)
            s+=a[D[p]];
        if (D[p]+k-1<=i)
            ++p;
    }
    fout<<s<<"\n";
    return 0;
}