#include<cstdio>
#include<deque>
#include<fstream>
#define NMAX 5000000
using namespace std;
long long res;
struct TYPE { int nr,ind; };
deque <TYPE> q;
TYPE make (int a, int b)
{
    TYPE res;
    res.nr=a;
    res.ind=b;
    return res;
}
int main()
{
    ifstream in ("deque.in");
    ofstream out ("deque.out");
    int n,k,i,val;
    TYPE aux;
    in >> n >> k;
    for(i=1;i<=k;i++)
    {
        in >> val;
        aux=make(val,i);
        while(!q.empty() && q.back().nr>=val)
            q.pop_back();
        q.push_back(aux);
    }
    res=(long long)q.front().nr;
    for(i=k+1;i<=n;i++)
    {
        in >> val;
        aux=make(val,i);
        while(!q.empty() && q.back().nr>=val)
            q.pop_back();
        q.push_back(aux);
        while(!q.empty() && q.front().ind<=i-k)
            q.pop_front();
        res+=(long long)q.front().nr;
    }
    out << res << '\n';
    return 0;
}