#include <fstream>
#include <deque>
using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

deque<pair<int,int>> q;

int main()
{
    long long sum=0;
    int i,n,a,k;
    cin>>n>>k;
    for(i=1;i<=n;i++){
        cin>>a;
        while(!q.empty() && q.back().first>=a) q.pop_back();
        q.push_back({a,i});
        if(i>=k){
            while(!q.empty() && q.front().second<=i-k) q.pop_front();
            sum+=1ll*q.front().first;
        }
    }
    cout<<sum;
    return 0;
}