#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[5000001],d[5000001];
int main()
{
    int n,k,st,dr,i;
    long long s=0;
    cin>>n>>k;
    st=0;
    dr=-1;
    for(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;
}