#include <fstream>
#include<queue>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n;long long s;
int v[5000005];
typedef pair <int,int> ii;
deque<ii> q;
int main()
{ int k;
in>>n>>k;
    for (register int i=1;i<=n;++i)
        in>>v[i];
    for(register int i=1;i<=n;++i)
    {
        while(!q.empty()&&q.back().first>=v[i])
        {
            q.pop_back();
        }
        q.push_back(ii(v[i],i));
        while(!q.empty()&&i-q.front().second+1>k)
            q.pop_front();
        if(i>=k)
            s=s+q.front().first;
    }
    out<<s;
    return 0;
}