1 #include <cstdio>
 2 #include <iostream>
 3 #define N 100010
 4 using namespace std;
 5 int n,ans,a[N],sum[N];
 6 int main()
 7 {
 8     scanf("%d",&n);
 9     for (int i=1;i<=n;i++) scanf("%d",&a[i]),sum[i]=sum[i-1]+a[i];
10     for (int i=1;i<=n-ans;i++)
11         for (int j=i+ans+1;j<=n;j+=2) 
12             if ((sum[j]-sum[i-1])*2==j-i+1)    ans=max(ans,j-i+1);
13     printf("%d",ans);
14 }