#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000002],dqe[5000002];
long long S=0;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;++i)f>>a[i];
    int b=0,e=1;
    for(int i=1;i<=n;++i)
    {
        while(e<=b&&a[i]<=a[dqe[b]])--b;
        ++b;dqe[b]=i;
        if(dqe[e]==i-k)++e;
        if(i>=k)S+=a[dqe[e]];
    }
    g<<S;
}