#include <bits/stdc++.h>

using namespace std;
const int MAX=5000007;
int n,k;
int64_t v[MAX];
deque <int> dq;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define cin fin
#define cout fout
int minn[MAX];
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;++i)
    {
        cin>>v[i];
    }
    for(int i=1;i<=k;++i)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }
    minn[0]=v[dq.front()];
    int64_t sum=minn[0];
    for(int i=k+1;i<=n;++i)
    {
        if(dq.front()<=i-k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && v[dq.back()]>v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        minn[i-k+1]=v[dq.front()];
        sum+=minn[i-k+1];
    }
    cout<<sum;
    return 0;
}