#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int N=5000001;
int v[N],d[N];
long long s;
int n,k,st,dr=-1;
int main()
{
    f>>n>>k;
    for(int i=0;i<n;i++){
        f>>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]];
        /*for(int j=st;j<=dr;j++)
            g<<v[d[j]]<<' ';
            g<<'\n';*/
    }
    g<<s;
    return 0;
}