#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,v[5000001],D[5000001],inc,sf;
long long s;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    inc=1; sf=0;
    for(i=1;i<=n;i++)
    {
        while(inc<=sf&&v[i]<=v[D[sf]]) sf--;
        D[++sf]=i;
        if(D[inc]==i-k) inc++;
        if(i>=k) s+=v[D[inc]];
    }
    fout<<s;
    return 0;
}