#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
const int NMAX = 5000001;
int v[NMAX], n, k;
long long sum;
deque<int> dq;

int main(int argc, const char * argv[]) {
    cin>>n>>k;
    for(int i=1; i<=n; i++)
    {
        cin>>v[i];
                
        while(!dq.empty() and v[i] <= v[dq.back()])
            dq.pop_back();
        
        dq.push_back(i);
        
        if(dq.front() < i - k + 1)
            dq.pop_front();
        
        if(i >= k)
            sum += v[dq.front()];
    }
    
    cout<<sum<<'\n';
    
    return 0;
}