#include <fstream>

using namespace std;

long long i, n, k, st=1, dr, s;
int v[5000002], d[5000002];

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>v[i];
    for(i=1; i<=n; i++)
    {
        while(st<=dr && v[d[dr]]>v[i])
            dr--;
        d[++dr]=i;
        if(i-k+1>d[st])
            st++;
        if(i>=k)
            s+=1ll*v[d[st]];
    }
    fout<<s;
}