#include <cstdio> int x = 1, y = 2; signed main() { getchar(); while (1) { switch (getchar()) { case '0': x = 3ll * x % 998244353, y = (y << 1) % 998244353; break; case '1': x = (3ll * x + 2 * y) % 998244353; break; default: printf("%d\n", (x + y) % 998244353); return 0; } } return 0; }