#include <fstream>
using namespace std;

ifstream cin ("deque.in");
ofstream cout("deque.out");

int v[5000005], d[5000005];

int main()
{
    int n,k,st,dr,i;
    long long s=0;
    cin>>n>>k;
    st=0;
    dr=-1;
    for(int i=0; i<=n; i++)
    {
        cin>>v[i];
        if(st<=dr && d[st]==i-k)
            st++;
        while(st<=dr && v[i]<=v[d[dr]])
            dr--;
        d[++dr]=i;
        if(i>=k-1)
            s+=v[d[st]];
    }
    cout<<s;
    return 0;
}