#include <fstream>
#include <cstdio>
#include <deque>
using namespace std;
FILE *fin=fopen("deque.in","r");
ofstream fout("deque.out");
int n,k,i,v[5000010];
long long s;
deque<int> dq;

int main()
{
fscanf(fin,"%d%d",&n,&k);
for(i=1;i<=k;i++)
{
    fscanf(fin,"%d",&v[i]);
    if(!dq.empty())
        while(v[i]<v[dq.back()])
        {
            dq.pop_back();
            if(dq.empty())
                break;
        }
    dq.push_back(i);
}
s=s+v[dq.front()];
for(i=k+1;i<=n;i++)
{
    fscanf(fin,"%d",&v[i]);
    if(!dq.empty() && dq.front()<=i-k)
        dq.pop_front();
    if(!dq.empty())
        while(v[i]<v[dq.back()])
        {
            dq.pop_back();
            if(dq.empty()==1)
                break;
        }
    dq.push_back(i);
    s=s+v[dq.front()];
}
fout<<s;

return 0;
}