#include <iostream>
#include <cstdio>
#include <algorithm>
#include <deque>
#define INF 0x3f3f3f3f
using namespace std;
deque <pair<int,int>> q;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    long long n,k,i,s=0,nr;
    scanf("%lld%lld",&n,&k);
    for(i=1;i<=n;i++){
        scanf("%lld",&nr);
        while(q.size() && q.front().second < i-k+1)
            q.pop_front();
        while(q.size() && nr <= q.back().first)
            q.pop_back();
        q.push_back({nr,i});
        if(i >= k)
        s += q.front().first;
    }
    printf("%lld",s);
    return 0;
}