#include<bits/stdc++.h>
using namespace std;
const int M = 998244353;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    int n;
    cin >> n;
    vector<int> a(n);
    vector<long long> pw(n + 1);
    pw[0] = 1;
    int inv = (M + 1) / 2;
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
        pw[i + 1] = pw[i] * inv % M;
    }
    long long ans = 0;
    for (int i = 0; i < n; ++i) {
        if (abs(a[i]) < 2) continue;
        vector<long long> c = { pw[min(i, 1)], 0 };
        int s = 1;
        for (int j = i - 1; j >= 0; --j) {
            s *= a[j];
            if (s == 1) {
                c[0] = (c[0] + pw[min(i, i - j + 1)]) % M;
            }
            else if (s == -1) {
                c[1] = (c[1] + pw[min(i, i - j + 1)]) % M;
            }
            else break;
        }
        int b = 1;
        for (int j = i; j < n; ++j) {
            b *= a[j];
            if (b == -2) {
                ans = (ans + c[0] * pw[min(n - i - 1, j - i + 1)]) % M;
            }
            else if (b == 2) {
                ans = (ans + c[1] * pw[min(n - i - 1, j - i + 1)]) % M;
            }
            else break;
        }
    }
    cout << ans << '\n';
    return 0;
}