#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> q;
long long S,x;
int n,i,k;
long long v[5000001];
int main()
{   f>>n>>k;
    for(i=1;i<=n;i++){
        f>>v[i];
        while(!q.empty()&&v[q.back()]>v[i])
            q.pop_back();
        q.push_back(i);
        if(i-q.front()>=k)
            q.pop_front();
        if(i>=k)
            S+=v[q.front()];
    }
    g<<S;
    return 0;
}