#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000005],d[5000005],dr,st
,i;
long long ans;
int main()
{
    f>>n>>k;
    for(i=1; i<=n; ++i)f>>v[i];
    for(i=1; i<=n; ++i)
    {
        while(dr>=st && v[d[dr]]>v[i])
            dr--;
        d[++dr]=i;
        if(d[st]==i-k)
            st++;
        if(i>=k)
            ans+=v[d[st]];
    }
    g<<ans<<'\n';
    return 0;
}