#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int maxn=5000010;

int a[maxn], deque[maxn], i, k, n, first, last;
long long ans;

int main()
{
    f>>n>>k;
    for(i=1; i<=n; ++i) f>>a[i];

    first=1, last=0;
    for(i=1; i<=n; ++i)
    {
        while(first<=last && a[i]<= a[deque[last]]) --last;
        deque[++last]=i;
        if(deque[first]==i-k) ++first;
        if(i>=k) ans+=a[deque[first]];
    }

    g<<ans<<"\n";
    return 0;
}