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

#define MOD 998244353

int main() {
	long long N; cin >> N;
	string S; cin >> S;

	vector<vector<long long>> dp1(N, vector<long long>(N, 0)), dp0(N, vector<long long>(N, 0));
	vector<vector<long long>> rui1(N, vector<long long>(N, 0)), rui0(N, vector<long long>(N, 0));

	for (int i = 0; i < N; i++) {
		for (int j = 0; j < N; j++) {
			if (j >= i && S[j - i] == '1') {
				if (j - i - 1 >= 0) dp1[i][j] = (rui0[i][j - i - 1] + rui1[i][j - 1]) % MOD;
				if (j - i - 1 >= 0) dp0[i][j] = (rui0[i][j - 1] - rui0[i][j - i - 1] + MOD) % MOD;
				dp1[i][j] += 1;
			}
			else if (j >= i && S[j - i] == '0') {
				if (j - i - 1 >= 0) dp1[i][j] = rui1[i][j - 1];
				if (j - i - 1 >= 0) dp0[i][j] = rui0[i][j - 1];
				dp0[i][j] += 1;
			}
			else if (j < i && j == 0) dp0[i][j] = 1;
			else dp0[i][j] = dp0[i][j - 1] * 2 % MOD;
 			if (j > 0) rui1[i][j] = rui1[i][j - 1];
			if (j > 0) rui0[i][j] = rui0[i][j - 1];
			rui1[i][j] = (rui1[i][j] + dp1[i][j]) % MOD;
			rui0[i][j] = (rui0[i][j] + dp0[i][j]) % MOD;
		}
	}

	long long ans = 0;
	long long pow2 = 1;
	for (int i = 0; i < N; i++) {
		ans += pow2 * dp1[i][N - 1];
		pow2 = pow2 * 2 % MOD;
	}
	cout << ans % MOD << endl;
}