#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000000];
int d[5000000];
int main()
{
    long long dr=-1, st=0, s=0,k, n;
    in>>n>>k;
    for(int i=0;i<n;++i) in>>v[i];
    for( int i=0; i<n; ++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;
}