#include <cstdio>
#include <deque>

using namespace std;

int main() {
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int i,n,k;
    long long int v[5001024],sol;
    deque <int> q;
    scanf("%d%d",&n,&k);
    for(i=1;i<k;++i) {
        scanf("%lld",&v[i]);
        for(;!q.empty()&&v[i]<v[q.back()];q.pop_back());
        q.push_back(i);
    }
    for(sol=0;i<=n;++i) {
        scanf("%lld",&v[i]);
        for(;!q.empty()&&v[i]<v[q.back()];q.pop_back());
        q.push_back(i);
        if(q.front()==i-k) {
            q.pop_front();
        }
        sol+=v[q.front()];
    }
    printf("%lld",sol);
    return 0;
}