#include <fstream>
#define N 5000010
using namespace std;
int val[N],q[N];

ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,x,b,t;
long long v;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>val[i];
    for(i=1;i<k;i++)
    {
        while(t&&val[q[t]]>=val[i])t--;
        q[++t]=i;
    }
    for(b=1;i<=n;i++)
    {
        while(t>=b&&val[q[t]]>=val[i])t--;
        q[++t]=i;
        if(q[b]==i-k)b++;
        v+=val[q[b]];
    }
    fout<<v;
    return 0;
}