#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
const int N = 5000001;
int v[N],d[N];
int main()
{
    int n,i,k,j,st,dr;
    long long s;
    in>>n>>k;
    st=0,dr=-1,s=0;
    for(i=0;i<n;i++)
    {
        in>>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]];
    }
    out<<s;
    return 0;
}