#include<bits/stdc++.h>
using namespace std;
const long long MaxN = 5e5 + 5;
long long n,a[MaxN],dp[MaxN][2];
int main()
{
    cin >> n;
    for (long long i=1; i<=n; i++)
    {
        cin >> a[i];
    }
    long long res=0;
    for (long long i=1; i<=n; i++)
    {
        dp[a[i]][0]=1;
        dp[a[i]][0]=max(dp[a[i]-1][0]+1,dp[a[i]][0]);
        if(a[i]-2>=0)
        {
            dp[a[i]][1]=max(dp[a[i]-2][0]+2,dp[a[i]][1]);
        }
        dp[a[i]][1]=max(dp[a[i]-1][1]+1,dp[a[i]][1]);
        res=max({res,dp[a[i]][0],dp[a[i]][1]});
    }
    cout << res;
}
 

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