JOI 2007 A Problem, Half of the Test Cases Do Not Go Through Even though the Algorithm Looks Correct

#include<bits/stdc++.h>
#define_GLIBCXX_DEBUG
# define rep(i,n) for (inti=0;i<n;i++)
# define reps(i,n) for (inti=1;i<=n;i++)
#define INF1e9
# define ALL(v) v. begin(), v. end()

using namespace std;
using ll = long long;


int main() {
  int n,k;
  cin>>n>>k;
  lls = 0;
  lla;

  queue<int>q;
  rep(i,k){
    cin>>a;
    s+=a;
    q.push(a);
  }

  llans=s;
  if(n>k){
    rep(i,n-k){
      cin>>a;
      s - = q.front();
      q.pop();
      s+=a;
      q.push(a);
      an=max(ans,s);
    }
  }
  cout<<ans;
}