#include<bits/stdc++.h>
using namespace std;

using ll=long long;

const int N=1e6+1e3+7;

const ll P=(1ll<<61)-1,bs=1313131;

ll mul(const ll &a,const ll &b)
{
    return (__int128)a*b%P;
}

ll hl[N],hr[N],pw[N];

int n,a[N],f[N],g[N];

int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    pw[0]=1;
    for(int i=1;i<=n;i++)
        pw[i]=mul(pw[i-1],bs);
    for(int i=1;i<=n;i++)
        hl[i]=(mul(hl[i-1],bs)+a[i])%P;
    for(int i=n;i>=1;i--)
        hr[i]=(mul(hr[i+1],bs)+a[i])%P;
    int ans=-1;
    for(int i=1;i<=n;i++)
        if(a[i]>a[i-1])
            f[i]=f[i-1]+1;
        else
            f[i]=1;
    for(int i=n;i>=1;i--)
        if(a[i]>a[i+1])
            g[i]=g[i+1]+1;
        else
            g[i]=1;
    for(int i=2;i<=n-1;i++)
    {
        if(a[i]<=a[i-1]||a[i]<=a[i+1])
            continue;
        int l=0,r=min(f[i],g[i]);
        while(r-l>1)
        {
            int mid=(l+r)>>1;
            if((hl[i]-mul(hl[i-mid-1],pw[mid+1])+P)%P==(hr[i]-mul(hr[i+mid+1],pw[mid+1])+P)%P)
                l=mid;
            else
                r=mid;
        }
        if(l)
            ans=max(ans,2*l+1);
    }
    printf("%d\n",ans);
}