Go: package main

import (
	"bufio"
	"fmt"
	"io"
	"math"
	"os"
	"strconv"
)

func main() {
	parseProblem(os.Stdin)
}

func parseProblem(r io.Reader) {
	const (
		initialBufSize = 100000
		maxBufSize     = 1000000
	)
	buf := make([]byte, initialBufSize)

	sc := bufio.NewScanner(r)
	sc.Buffer(buf, maxBufSize)
	sc.Split(bufio.ScanWords) // bufio.ScanLines
	for true {
		n, k := scanInt(sc), scanInt(sc)
		if n == 0 && k == 0 {
			break
		}
		sum := make([]int, n+2)
		for i := 2; i <= n+1; i++ {
			sum[i] = sum[i-1] + scanInt(sc)
		}
		max := math.MinInt32
		for i := 1; i+k <= n+1; i++ {
			if v := sum[i+k] - sum[i]; max < v {
				max = v
			}
		}
		fmt.Println(max)
	}
	return
}

func resolve(n int) int {
	return n
}

// snip-scan-funcs
func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	i, _ := strconv.Atoi(sc.Text())
	return int(i)
}
func scanString(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

C++: #include<bits/stdc++.h>
using namespace std;

template<class T>
struct treap{
    #define treapInf INT_MAX

public:
    struct node{
        T val;
        node *lch,*rch;
        int pri,sz;
        T sum,mini;

        node(T val,int pri):val(val),pri(pri),sz(1),sum(val),mini(val){
            lch=rch=NULL;
        }
    };

    node *root;
    treap():root(NULL){srand(time(NULL));}

private:

    inline int size(node *t){return !t?0:t->sz;}
    inline T sum(node *t){return !t?0:t->sum;}
    inline T mini(node *t){return !t?treapInf:t->mini;}

    node *update(node *t){
        if(!t)return t;
        t->sz=size(t->lch)+size(t->rch)+1;
        t->sum=sum(t->lch)+sum(t->rch)+t->val;
        t->mini=min(min(mini(t->lch),mini(t->rch)),t->val);
        return t;
    }

    node *merge(node *l,node *r){
        if(!l||!r)return l?l:r;

        if(l->pri>r->pri){
            l->rch=merge(l->rch,r);
            return update(l);
        }
        else{
            r->lch=merge(l,r->lch);
            return update(r);
        }
    }

    pair<node *,node *>split(node *t,int k){
        if(!t)return make_pair((node *)NULL,(node *)NULL);

        if(k<=size(t->lch)){
            pair<node *,node *>s=split(t->lch,k);
            t->lch=s.second;
            return make_pair(s.first,update(t));
        }
        else{
            pair<node *,node *>s=split(t->rch,k-size(t->lch)-1);
            t->rch=s.first;
            return make_pair(update(t),s.second);
        }
    }

    node *insert(node *t,int k,T val,int pri){
        pair<node *,node *>s=split(t,k);
        t=merge(s.first,new node(val,pri));
        t=merge(t,s.second);
        return update(t);
    }

    node *erase(node *t,int k){
        pair<node *,node *>s1,s2;
        s2=split(t,k+1);
        s1=split(s2.first,k);
        return update(t=merge(s1.first,s2.second));
    }

    node *find(node *t,int k){
        //if(!t)return t;
        int c=size(t->lch);
        if(k<c)return find(t->lch,k);
        if(k==c)return t;
        return find(t->rch,k-c-1);
    }

    T rangeMinimumQuery(int l,int r,node *t){
        int sz=size(t);
        if(r<=0||sz<=l)return treapInf;
        if(l<=0&&sz<=r)return mini(t);

        sz=size(t->lch);
        T vl=rangeMinimumQuery(l,r,t->lch);
        T vr=rangeMinimumQuery(l-sz-1,r-sz-1,t->rch);
        T res=min(vl,vr);
        if(l<=sz&&sz<r)res=min(res,t->val);
        return res;
    }

    T rangeSumQuery(int l,int r,node *t){
        int sz=size(t);
        if(r<=0||sz<=l)return 0;
        if(l<=0&&sz<=r)return sum(t);

        sz=size(t->lch);
        T vl=rangeSumQuery(l,r,t->lch);
        T vr=rangeSumQuery(l-sz-1,r-sz-1,t->rch);
        T res=vl+vr;
        if(l<=sz&&sz<r)res+=t->val;
        return res;
    }

    void debug(node *t){
        if(!t)return;
        debug(t->lch);
        cout<<t->val<<" ";
        debug(t->rch);
    }

public:

    void insert(int k,T val){root=insert(root,k,val,rand());}
    void erase(int k){root=erase(root,k);}
    node *find(int k){return find(root,k);}

    void add(int k,T v){
        node *a=find(k);
        T tmp=a->val;
        erase(k);
        insert(k,tmp+v);
    }

    void update(int k,T v){
        erase(k);
        insert(k,v);
    }

    T rangeMinimumQuery(int l,int r){
        return rangeMinimumQuery(l,r,root);
  }


    T rangeSumQuery(int l,int r){
        return rangeSumQuery(l,r,root);
    }

    void init(int n,T val){
        for(int i=0;i<n;i++)insert(i,val);
    }

    void debug(){
        debug(root);
        cout<<endl;
    }
};


int main(){

    int N,K;
    while(cin>>N>>K,N||K){
        treap<long long>t;
        for(int i=0;i<N;i++){
            int a;cin>>a;
            t.insert(i,a);
        }

        long long ma=LLONG_MIN;

        for(int i=0;i+K<=N;i++){
            ma=max(ma,t.rangeSumQuery(i,i+K));
        }

        cout<<ma<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <algorithm>

using namespace std;

int main() {
    while(true){
    int n,k,max=-1e9,sum=0;
    cin >> n >> k;
        if(n==0) break;
    int ar[n];
    for(int i = 0;i<n;i++){
        int a;
        cin >> a;
        ar[i]=a;
    }
    
    for(int i=0;i<n-k+1;i++){
        for(int j=0;j<k;j++){
            sum += ar[i+j];
        }
    if(sum>max){
        max=sum;
    }
        sum=0;
    }
    cout << max <<endl;
    }
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
using namespace std;
using ll = long long;
const ll INF = 1LL << 60;

int main() {
    int N, K;
    while(cin >> N >> K) {
        if(N == 0) break;
        vector<ll> a(N);
        for(int i = 0; i < N; ++i) cin >> a[i];

        vector<int> s(N+1, 0);
        for(int i = 0; i < N; ++i) s[i+1] = s[i] + a[i];

        ll res = -INF;
        for(int i = 0; i <= N-K; ++i) {
            ll val = s[K+i];
            if(res < val) res = val;
        }
        cout << res << endl;
    }

}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
using namespace std;
using ll = long long;
const int INF = 999999999999;

vector<ll> ret;

void solve(vector<ll>& a, ll k) {
    ll n = a.size();
    vector<ll> cs(n+1, 0);
    for(int i = 1; i < n+1; i++) {
        cs[i] = cs[i-1];
        cs[i] += a[i-1];
    }

    ll ans = (-1) * INF;
    for(int i = 0; i < n+1; i++) {
        ll now = cs[i+k] - cs[i];
        ans = max(ans, now);
    }
    ret.push_back(ans);
}

int main() {
    do {
        ll n, k;
        cin >> n >> k;
        if (n == 0 && k == 0) break;
        vector<ll> a(n, 0);
        for(int i = 0; i < n; i++) cin >> a[i];
        solve(a, k);
    } while(true);

    for(auto &r : ret) {
        cout << r << endl;
    }
}

C++: import sys

#fp = open("input.txt", "r")
fp = sys.stdin

while True:
    req = map(int, fp.readline()[:-1].split(" "))
    if req[0] + req[1] == 0:
        break

    n = req[0]
    k = req[1]

    sum_max = 0
    num_list = []
    
    for i in xrange(n):
        num = int(fp.readline()[:-1])
        num_list.append(num)
        if k > 0:
            sum_max += num
            k -= 1
            continue
        else:
            num_list.pop(0)
            sum_tmp = sum(num_list)
            if sum_tmp > sum_max:
                sum_max = sum_tmp

    print sum_max