#include <fstream>
#define NMAX  5000000
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

int n, k, x;
int d[NMAX+2], p=1, u, v[NMAX+2];
long long s;
int main()
{
    fin>>n>>k;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(int i=1; i<=n; i++)
    {
        ///minimul unei subsecvente care se termina pe poz i de lungime k
        while(p<=u && v[i]<=v[d[u]])
            u--;
        d[++u]=i;
        if(i>=k)
            s+=v[d[p]];
        if(i-d[p]+1==k)
            p++;

    }
    fout<<s<<" ";





    return 0;
}