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<iostream>
#include<vector>
using namespace std;
int main(){
    while(1){
    int n,k;
    cin >> n >> k;
    if(n==0 && k==0){
        break;
    }
    vector<int>a(n);
    for(int i=0; i<n; i++){
        cin >> a[i];
    }
    int s=0;
    int m=0;

    while(s+k-1<n){
        int cm=0;
        for(int j=0; j<k; j++){
            cm+=a[s+j];
        }
    if(cm>m){
        m=cm;
    }
    s++;
    }
    cout << m << endl;
    }
}

C++: #include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iterator>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
#include <fstream>
#include <iomanip>
#include <cassert>
//#include <utility>
//#include <memory>
//#include <functional>
//#include <deque>
//#include <cctype>
//#include <ctime>
//#include <numeric>
//#include <list>
//#include <iomanip>

//#if __cplusplus >= 201103L
//#include <array>
//#include <tuple>
//#include <initializer_list>
//#include <forward_list>
//
//#define cauto const auto&
//#else

//#endif

using namespace std;


typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()
#define DEBUG
#ifdef DEBUG
#define dump(x)  cout << #x << " = " << (x) << endl;
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#else
#define dump(x) 
#define debug(x) 
#endif

#define MOD 1000000007LL
#define EPS 1e-8
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
#define maxs(x,y) x=max(x,y)
#define mins(x,y) x=min(x,y)

void mainmain(){
	int n;
	int K;
	while(cin>>n>>K,n){
		vll v(n);
		rep(i,n) cin>>v[i];
		ll cnt=0;
		ll ans=-INFL;
		ll sum=0;
		rep(i,n){
			if(cnt<K){
				sum+=v[i];
				cnt++;
			}
			else{
				sum+=v[i]-v[i-K];
				maxs(ans,sum);
			}
		}
		cout<<ans<<endl;
	}
}


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout<<fixed<<setprecision(20);
    mainmain();
}

C++: #include <bits/stdc++.h>
#define FOR(i,n) for(int i=0;i<(int)(n);i++)
#define FORR(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define pb(a) push_back(a)
#define mp(x,y) make_pair(x,y)
#define ALL(a) a.begin(),a.end()
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,-1,sizeof(a))
#define len(a) sizeof(a)
#define ll long long
#define pii pair<int,int>
#define INF 1<<29
#define MAX 101010
using namespace std;

int n,k,a[MAX],sum[MAX];

void solve(){
 for(;;){
  cin>>n>>k;
  if(!n) break;
  FOR(i,n) cin>>a[i];
  FOR(i,n) sum[i+1]=sum[i]+a[i];
  int ma=0;
  FOR(i,n-k) ma=max(ma,sum[i+k]-sum[i]);
  cout<<ma<<endl;
 }
}

int main(){
 solve();
 return 0;
}

C++: #include <iostream>
#include <vector>
#include <array>
#include <set>
#include <string>
#include <numeric>
#include <algorithm>

#define rep(i, n) for(int i = 0; i < n; i++)



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

    for(;;) {
        int n, k;
        std::cin >> n >> k;
        if (n == 0 && k == 0) break;
        std::vector<int> num(n);
        rep(i, n) std::cin >> num.at(i);

        long long int sum = std::accumulate(num.begin(),num.begin()+k,0);
        rep(i,n-k) sum = std::max(sum,sum-num.at(i)+num.at(k+i));

        std::cout << sum << "\n";
    }

    return 0;
}

C++: #include <iostream>
#include <algorithm>
#define N 100000
using namespace std;
int main(){
  int n,k,in[N],maxv,sum,i;
  while(1){
    cin >> n >> k;
    if(n==0&&k==0) break;
    maxv=-2000000;
    sum=0;
    for(i=0;i<n;i++){
      cin >> in[i];
      sum+=in[i];
      if(i>=k) sum-=in[i-k];
      maxv=max(maxv,sum);
    }
    cout << maxv << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;
int main() {
	int n, k;
	while (cin >> n >> k&&n != 0 && k != 0) {
		int a[100000], sum = 0;
		for (int i = 0; i < n; i++) {
			cin >> a[i];
			if (i < k) sum += a[i];
		}
		int s = 1, e = k, f;
		while (e < n) {
			f = sum;
			sum += a[e];
			sum -= a[s - 1];
			sum = max(sum, f);
			s++;
			e++;
		}
		cout << sum << endl;
	}
}

C++: #include<string>
#include<cstdio>
#include<cctype>
#include<iostream>
#include <algorithm>
#include<cmath>
#include<queue>
using namespace std;

int main(){
    while(1){
    int n=0,k=0,num[100010]={0},ans=0,sum=0;
    cin>>n>>k;
    if(n==0 && k==0)break;
    for(int i=0;i<n;i++){
            cin>>num[i];
            if(i<k){
            sum+=num[i];
            }
        }
    for(int i=1;i<n-2;i++){
        int s;
        s=sum-num[i-1]+num[i+k-1];
        //s???sum????????????????¶????
        sum=s;
        //sum????????¨??????
        if(sum>ans)ans=sum;
        }
    cout<<ans<<endl;
    }
    return 0;
}

C++: 
#include<iostream>
main(){
  for(int n,k,a[100000],s,M,i;std::cin>>n>>k,n;printf("%d\n",M)){
    for(i=s=0;i<n;i++<k&&(M=s+=a[i-1]))std::cin>>a[i];
    for(i=k;i<n;M<s&&(M=s))s+=a[i]-a[i++-k];
  }
}

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{
        ans=max(ans,sum);
        sum-=a[i-k];
        sum+=a[i];
        ans=max(ans,sum);
      }
    }
    cout<<ans<<endl;
  }
}

C++: #include<iostream>
using namespace std;
long su[100000010] = { 0 };
long sai;
int main()
{
	long n, k;
	long i, j;
	long a;
	while (cin >> n >> k, n != 0 && k != 0)
	{
		for (i = 1; i <= n; i++)
		{
			cin >> a;
			su[i] = su[i - 1] + a;
		}
		sai = 0;
		for (i = k; i <= n; i++)
		{
			if (sai < su[i] - su[i - k])
			{
				sai = su[i] - su[i - k];
			}
		}
		cout << sai << endl;
	}
	return 0;
}