#include <bits/stdc++.h>
using namespace std;
int dp[511][511],cnt[511],f[511][511],n,a[511],fac[511],ifac[511],iv[511];
const int p=998244353;
inline int qpow(int bs,int ex){int ans=1;while(ex){if(ex&1)ans=1ll*ans*bs%p;ex>>=1;bs=1ll*bs*bs%p;}return ans;}
int b[511];
int main()
{
	scanf("%d",&n);for(int i=1;i<=n;++i)scanf("%d",a+i);
	for(int i=1;i<=n;++i)b[i]=b[i-1]+(a[i]!=a[i-1]);
	for(int i=1;i<=n;++i)a[i]=b[i];
	fac[0]=1;for(int i=1;i<=n;++i)fac[i]=1ll*fac[i-1]*i%p;
	ifac[n]=qpow(fac[n],p-2);for(int i=n-1;~i;--i)ifac[i]=1ll*ifac[i+1]*(i+1)%p;
	for(int i=1;i<=n;++i)iv[i]=qpow(i,p-2);
	for(int l=n;l;--l)
	{
		for(int r=l;r<=n;++r)
		{
			for(int k=l+1;k<=r;++k)dp[l][r]=(dp[l][r]-1ll*f[k][r]*dp[l][k-1])%p;
			if(a[l]==a[r])f[l][r]=1;
			else if(a[l]+1==a[r])
			{
				int cl=0;
				for(int i=l;i<=r;++i)if(a[i]==a[l])++cl;
				f[l][r]=1ll*fac[r-l+1]*ifac[cl]%p*ifac[r-l+1-cl]%p;
			}
			else
			{
				f[l][r]=-2*dp[l][r]%p;
				if(a[r-1]==a[r])f[l][r]=(f[l][r]-f[l][r-2])%p;
				if(a[l]==a[l+1])f[l][r]=(f[l][r]-f[l+2][r])%p;
			}
			dp[l][r]=(dp[l][r]+f[l][r])%p;
		}
	}
	printf("%d\n",(f[1][n]%p+p)%p);
}