#include <fstream>
#include <deque>
#define indice first
#define valoare second
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>> Q;
int n,k,i,v;
long long sum;
int main()
{
    f>>n>>k;
    for(i=1;i<k;i++)
    {
        f>>v;
        while(Q.size()&&Q.back().valoare>=v)
            Q.pop_back();
        Q.push_back(make_pair(i,v));
    }
    for(i=k;i<=n;i++)
    {
        f>>v;
        while(Q.size()&&Q.back().valoare>=v)
            Q.pop_back();
        Q.push_back(make_pair(i,v));
        if(Q.front().indice==i-k)
            Q.pop_front();
        sum+=Q.front().valoare;
    }
    g<<sum;
    return 0;
}