#include<bits/stdc++.h>
using namespace std;
#define TASK "lcm"
const int N = 55;
int n,m,a[N];
namespace sub1
{
bool check()
{
return (n<=50 && m<=50);
}
int b[N];
bool check(int l, int r)
{
bool ok=1;
for(int i=l;i<=r;++i) ok&=(a[i]==a[r+l-i]);
return ok;
}
void solve()
{
for(int i=1;i<=n;++i) b[i]=a[i];
int ans=0;
for(int lo=1;lo<=n;++lo) for(int hi=lo;hi<=n;++hi)
{
sort(a+lo,a+hi+1);
for(int l=1;l<=n;++l) for(int r=l;r<=n;++r) ans=max(ans,check(l,r)*(r-l+1));
for(int i=lo;i<=hi;++i) a[i]=b[i];
}
cout<<ans;
}
}
void solve()
{
cin>>n>>m;
for(int i=1;i<=n;++i) cin>>a[i];
if(sub1::check()) return void(sub1::solve());
}
int main(void)
{
// freopen(TASK".inp","r",stdin);
// freopen(TASK".out","w",stdout);
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int testcase=1;
// cin>>testcase;
while(testcase--)
solve();
return 0;
}
