#include <bits/stdc++.h>
using namespace std;
/// poz val
deque<pair<int,int> > D;
int main(){
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k;
    scanf("%d %d",&n,&k);
    long long S=0;
    for(int i=1;i<=n;++i){
        int x;
        scanf("%d",&x);
        while(!D.empty()&&D.back().second>=x)
            D.pop_back();
        D.push_back({i,x});
        if(i>=k){
            S+=D.front().second;
            if(D.front().first==i-k+1)
                D.pop_front();
        }
    }
    printf("%lld\n",S);
    return 0;
}