#include <iostream>
#include <cstdio>
#include <deque>

using namespace std;

int v[5000002];
deque < pair < int , int > > q;

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    int n,k;
    long long sol=0;
    scanf("%d %d", &n, &k);
    for(int i=1;i<=n;i++)
        scanf("%d", &v[i]);
    for(int i=1;i<=k-1;i++)
    {
        int x=v[i];
        while(!q.empty() && q.back().first>=x)
            q.pop_back();
        q.push_back(make_pair(x,i));
    }
    for(int i=k;i<=n;i++)
    {
        int x=v[i];
        while(!q.empty() && q.back().first>=x)
            q.pop_back();
        if(!q.empty() && q.front().second<=i-k)
            q.pop_front();
        q.push_back(make_pair(x,i));
        long long val=q.front().first;
        sol+=val;
    }
    printf("%I64d\n", sol);
    fclose(stdin);
    fclose(stdout);
    return 0;
}