#include <iostream>
#include <deque>
#include <set>
using namespace std;

multiset<long long> minim;
long long n, k, value[5000001];
signed main(){
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    cin>>n>>k;
    for (long long i=0; i<k; ++i){
        cin>>value[i];
        minim.insert(value[i]);
    }
    long long sum=0;
    for (long long i=k; i<n; ++i){
        cin>>value[i];
        sum+=*minim.begin();
        //cout<<" - "<<*minim.begin()<<" - \n";
        minim.erase(value[i-k]);
        minim.insert(value[i]);
    }
    cout<<sum+*minim.begin();
    return 0;
}