#include <fstream>

using namespace std;

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

int n, i, k, v[5000001], d[5000001], p, u;
long long s;

int main(){
    fin>>n>>k;
    p = u = 1;
    fin>>v[1];
    d[1] = 1;
    for(i=2;i<=n;i++){
        fin>>v[i];
        while(p<=u && v[i] < v[d[u]])
            u--;
        d[++u] = i;
        if(i - d[p] == k)
            p++;
        if(i >= k)
            s += v[d[p]];
    }
    fout<<s;
    return 0;
}