#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");


deque <int> dq;
long long a[5000137];
int n,k;

int main()
{int i;
 fin>>n>>k;
 int f,b;
 long long s=0;
 for(i=1;i<=n;++i)
     fin>>a[i];
 f=1; b=0;
 for(i=1;i<=n;++i)
    {while(f<=b && a[i]<=a[dq[b]])
           b--;
     dq[++b]=i;
     if(dq[f]==i-k) f++;
     if(i>=k)
        s+=a[dq[f]];
    }
 fout<<s;




    return 0;
}