#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
#define N 5000001
int n,k,i=1,j,Q[N],a[N],L,R;
long long s;
int main()
{
    for(f>>n>>k;i<=n;++i) {
        for(f>>a[i];L<=R&&a[Q[R]]>=a[i];--R);
        Q[++R]=i;
        if(i-Q[L]==k)
            ++L;
        if(i>=k)
            s+=a[Q[L]];
    }
    g<<s;
    return 0;
}