#include<cstdio>
#include<deque>
using namespace std;
const int N=5000001;
deque<int>d;
int v[N];
long long s;
int n,k;
void scan(){
    int i;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
}
void init(){
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scan();
}
void solve(){
    int i;
    for(i=1;i<=n;i++){
        while(!d.empty()&&v[i]<=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)
            s+=v[d.front()];
    }
}
int main(){
    init();
    solve();
    printf("%lld",s);
    return 0;
}