#include <stdio.h>

#define MAXN 500005
#define MOD 998244353

int N;
char A[MAXN];
int can1[MAXN], can0[MAXN];

int main() {
    scanf("%d", &N);
    scanf("%s", A + 1);

    // suffix: can become 1
    can1[N+1] = 0;
    for (int i = N; i >= 1; i--) {
        can1[i] = can1[i+1] || (A[i] == '1');
    }

    // prefix: can become 0
    can0[0] = 0;
    for (int i = 1; i <= N; i++) {
        can0[i] = can0[i-1] || (A[i] == '0');
    }

    long long ans = 0;

    // count monotonic strings
    for (int k = 0; k <= N; k++) {
        int ok = 1;

        if (k > 0 && !can1[k]) ok = 0;
        if (k < N && !can0[k+1]) ok = 0;

        if (ok) ans++;
    }

    // check if original is monotonic (no "01")
    int monotonic = 1;
    for (int i = 1; i < N; i++) {
        if (A[i] == '0' && A[i+1] == '1') {
            monotonic = 0;
            break;
        }
    }

    // if original is NOT monotonic, add it
    if (!monotonic) ans++;

    printf("%lld\n", ans % MOD);
    return 0;
}