#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001],c[5000001];
int main()
{
    int n,k,sf=0,inc=1,i,s=0;
    v[0]=-10000006;
    in>>n>>k;
    for(i=1;i<=n;++i)
    {
        in>>v[i];
        if(i<k)
        {
            while(v[i]<v[c[sf]]&& inc<=sf)
                --sf;
            c[++sf]=i;
        }
        else
        {
            if(i-k+1>c[inc])
                ++inc;
            while(v[i]<v[c[sf]] && inc<=sf)
                --sf;
            c[++sf]=i;
            s+=v[c[inc]];

        }
    }
    out<<s;
    return 0;
}