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;
    cin>>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 <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef pair<int,int> P;
typedef long long ll;
const int INF=1e9;
int main(){
  ll n,k;
  ll a[100100];
  while(cin>>n>>k&&(n||k)){
    REP(i,n)cin>>a[i];
    ll sum=0,ans=0;
    REP(i,n){
      if(i<k){
        sum+=a[i];
      }else{
        sum-=a[i-k];
        sum+=a[i];
      }
      ans=max(ans,sum);
    }
    cout<<ans<<endl;
  }
}

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

using namespace std;

typedef long long ll;

ll solve(int n, int k) {
    ll a[n+1];
    a[0] = 0LL;
    for(int i=1;i<=n;++i){
        cin >> a[i];
        a[i] += a[i-1];
    }

    ll ans = -(1 << 60);
    for(int i=1;i<=n-k;++i) {
        ans = max(ans, a[i+k-1]-a[i-1]);
    }
    return ans;
}

int main() {
    int n, k;

    while(cin >> n >> k && n) {
        cout << solve(n, k) << endl;
    }
}

C++: #include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
int m[100000][2];
int main(){
while(1){
int n,k,i,j,x=0;
cin>>n>>k;
if(n==0&&k==0)break;
for(i=0;i<n;i++)cin>>m[i][0];
m[0][1]=m[0][0];
for(i=1;i<n;i++){
m[i][1]=m[i-1][1]+m[i][0];
}
for(i=k-1;i<n;i++){
x=max(x,m[i][1]-m[i-k][1]);
}
cout<<x<<endl;
return 0;
}
}

C++: #include <iostream>
#include <algorithm>
#include <string>
#include <stdio.h>
#include <queue>
#include <stack>
#include <math.h>
using namespace std;
int main(void)
{
	for (;;)
	{
		int a,b,c,d,max=0;
		scanf("%d %d",&a,&b);
		int e[a];
		if (a==0&&b==0) break;
		for (c=0;c<a;c++){
			scanf("%d",&d);
			e[c]=d;
		}
		for (int f=0;f<=a-b;f++){
			for (int g=1;g<b;g++){
				e[f]=e[f]+e[f+g];
			}
			if (e[f]>=max) max=e[f];
		}
		printf("%d\n",max);
	}
	return 0;
}

C++: #include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "unordered_map"
#include "unordered_set"
#include "iomanip"
#include "cmath"
#include "random"
#include "bitset"
#include "cstdio"
#include "numeric"

using namespace std;

const int MOD = 1000000007;
//const int MOD = 998244353;

long long int N, M, K, H, W, L, R;
//int N, M, K, H, W, L, R;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> N >> K;
	while(N){
	    vector<int>v(N + 1);
	int ans = -MOD;
	for (int i = 1; i <= N; i++) {
		cin >> v[i];
		v[i] += v[i - 1];
		if (i >= K) {
			ans = max(ans, v[i] - v[i - K]);
		}
	}
	cin>>N>>K;
	cout << ans << endl;
	}
}

C++: //https://onlinejudge.u-aizu.ac.jp/challenges/sources/JOI/Final/0516?year=2007

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n, k;

    while (cin >> n >> k, n | k) {
        vector<int> a((unsigned) n);
        for (int i = 0; i < n; ++i) {
            cin >> a[i];
        }

        int s = accumulate(a.begin(), a.begin() + k, 0);
        int ans = s;
        for (int i = k; i < n; ++i) {
            s += a[i] - a[i - k];
            ans = max(ans, s);
        }

        cout << ans << endl;
    }
    return 0;
}

/*
 *
 */