#include<cstdio>
#include<deque>
#define FOR(i,a,b)\
   for(int i=a; i<=b; ++i)
#define infile "deque.in"
#define outfile "deque.out"
#define nMax 5000005
using namespace std;

deque < int > Deck;

int v[nMax];

int N, K;

long long Sum;


void read(){
    freopen(infile, "r", stdin);

    scanf("%d %d", &N, &K);

    FOR(i,1,N)
        scanf("%d", &v[i]);

    fclose(stdin);
}

void solve(){
    FOR(i,1,N){
        while(!Deck.empty() && v[i] <= v[Deck.back()])
             Deck.pop_back();

        Deck.push_back(i);

        while(Deck.front() <= i-K)
            Deck.pop_front();

        if(i >= K)
           Sum += v[Deck.front()];
    }
}

void print(){
    freopen(outfile, "w", stdout);

    printf("%lld\n", Sum);

    fclose(stdout);
}

int main(){
    read();
    solve();
    print();

    return 0;
}