#include <fstream>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
const int nm=5000005;
int n,k,v[nm],d[nm],st,dr;
long long s;
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>v[i];
        if(st<=dr and d[st]==i-k)
            st++;
        while(st<=dr and v[i]<=v[d[dr]])
            dr--;
        d[++dr]=i;
        if(i>=k)
            s+=v[d[st]];
    }
    cout<<s;
    return 0;
}