#include<bits/stdc++.h>

#define int long long int
#define rep(a,b,c) for(int a=b;a<c;a++)
#define repm(a,b,c) for(int a=(b-1);a>=c;a--)
#define pb push_back
#define str string
#define sf(a) scanfs("%d",&a)
#define pb push_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) (v).begin(), (v).end()

using namespace std;

const int INF = 1e18 + 9;
const int Mod = 1e9 + 7;
inline int replac(str s){double ans=0;rep(i,0,s.length()){ans+=(s[i]-'0')*pow(10,s.length()-i-1);}return (int)ans;}
inline string numstr(int m){str s="";while(m>0){char c;int a=m/10;if(a>0)a=m%(a*10);else a=m;c=(char)('0'+a);s+=c;m/=10;}str st="";for(int i=s.size()-1;i>=0;i--){st+=s[i];}return st;}
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef vector<pii> vii;

signed main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    int m[100005];
    bool mm[100005];
    cin >> n ;
    rep(i,0,n){
        cin >> mm[i];
    }
    mm[n]=2;
    int mae=0;
    vector<int> u;
    u.pb(0);
    rep(i,0,n){
        if(mm[i]==mm[i-1]){
            u.pb(mae);
            mae=0;
        }
        mae++;
    }
    u.pb(mae);
    u.pb(0);
    int ans=0;
    //for(int v: u)cout << v << " ";
    rep(i,0,u.size()-2){
        ans=max(ans,u[i]+u[i+1]+u[i+2]);
    }
    cout << ans << endl;
    return 0;
}