#include <fstream>

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