#include <fstream>
#define ll long long

using namespace std;

ifstream cin ("deque.in");
ofstream cout ("deque.out");

int n,m,i,a,v[5000001],first,last,x[5000001];
ll sum=0;
int main()
{
    cin>>n>>m;
    first=1;
    last=0;
    for (i=1;i<=n;++i)
    {
        cin>>x[i];
    }
    //v[1]=1;
    for (i=1;i<=n;++i)
    {
        a=x[i];
        while (first<=last && x[v[last]]>a) --last;
        v[++last]=i;
        if (i>=m)
        {
            if (v[first]<=i-m) first++;
            sum+=x[v[first]];
        }
    }

    cout<<sum;
    return 0;
}