#include #include const int Mod = 998244353; int bit[21], bit_inv[21], root[21], root_inv[21]; long long div_mod(long long x, long long y, long long z) { if (x % y == 0) return x / y; else return (div_mod((1 + x / y) * y - x, (z % y), y) * z + x) / y; } long long pow_mod(int n, int k) { long long N, ans = 1; for (N = n; k > 0; k >>= 1, N = N * N % Mod) if (k & 1) ans = ans * N % Mod; return ans; } void NTT(int k, int a[], int z[]) { if (k == 0) { z[0] = a[0]; return; } int i, d = bit[k-1], tmpp; long long tmp; static int *b[21] = {}, *c[21] = {}, *x[21] = {}, *y[21] = {}; if (b[k] == NULL) { b[k] = (int*)malloc(sizeof(int) * d); c[k] = (int*)malloc(sizeof(int) * d); x[k] = (int*)malloc(sizeof(int) * d); y[k] = (int*)malloc(sizeof(int) * d); } for (i = 0; i < d; i++) { b[k][i] = a[i*2]; c[k][i] = a[i*2+1]; } NTT(k - 1, b[k], x[k]); NTT(k - 1, c[k], y[k]); for (i = 0, tmp = 1; i < d; i++, tmp = tmp * root[k] % Mod) { tmpp = tmp * y[k][i] % Mod; z[i] = x[k][i] + tmpp; if (z[i] >= Mod) z[i] -= Mod; z[i+d] = x[k][i] - tmpp; if (z[i+d] < 0) z[i+d] += Mod; } } void NTT_reverse(int k, int z[], int a[]) { if (k == 0) { a[0] = z[0]; return; } int i, d = bit[k-1], tmpp; long long tmp; static int *b[21] = {}, *c[21] = {}, *x[21] = {}, *y[21] = {}; if (b[k] == NULL) { b[k] = (int*)malloc(sizeof(int) * d); c[k] = (int*)malloc(sizeof(int) * d); x[k] = (int*)malloc(sizeof(int) * d); y[k] = (int*)malloc(sizeof(int) * d); } for (i = 0; i < d; i++) { x[k][i] = z[i*2]; y[k][i] = z[i*2+1]; } NTT_reverse(k - 1, x[k], b[k]); NTT_reverse(k - 1, y[k], c[k]); for (i = 0, tmp = 1; i < d; i++, tmp = tmp * root_inv[k] % Mod) { tmpp = tmp * c[k][i] % Mod; a[i] = b[k][i] + tmpp; if (a[i] >= Mod) a[i] -= Mod; a[i+d] = b[k][i] - tmpp; if (a[i+d] < 0) a[i+d] += Mod; } } void prod_poly_NTT(int da, int db, int a[], int b[], int c[]) { int i, k; for (k = 0, bit[0] = 1; bit[k] < da + db - 1; k++) bit[k+1] = bit[k] * 2; for (i = k - 1, bit_inv[k] = div_mod(1, bit[k], Mod); i >= 0; i--) bit_inv[i] = bit_inv[i+1] * 2 % Mod; for (i = k - 1, root[k] = pow_mod(3, (Mod - 1) / bit[k]), root_inv[k] = pow_mod(3, Mod - 1 - (Mod - 1) / bit[k]); i >= 0; i--) { root[i] = (long long)root[i+1] * root[i+1] % Mod; root_inv[i] = (long long)root_inv[i+1] * root_inv[i+1] % Mod; } int *x = (int*)malloc(sizeof(int) * bit[k]), *y = (int*)malloc(sizeof(int) * bit[k]), *z = (int*)malloc(sizeof(int) * bit[k]); NTT(k, a, x); NTT(k, b, y); for (i = 0; i < bit[k]; i++) z[i] = (long long)x[i] * y[i] % Mod; NTT_reverse(k, z, c); for (i = 0; i < da + db - 1; i++) c[i] = (long long)c[i] * bit_inv[k] % Mod; free(x); free(y); free(z); } int main() { int i, N; char S[300001]; scanf("%d", &N); scanf("%s", S); int a[1048576] = {}, b[1048576] = {}, c[1048576] = {}; for (i = 0; i < N; i++) { if (S[i] == 'i') a[N-i-1] = 1; else b[i] = 1; } prod_poly_NTT(N, N, a, b, c); long long ans = 0, fact[300001], fact_inv[300001]; for (i = 1, fact[0] = 1; i <= N; i++) fact[i] = fact[i-1] * i % Mod; for (i = N - 1, fact_inv[N] = div_mod(1, fact[N], Mod); i >= 0; i--) fact_inv[i] = fact_inv[i+1] * (i + 1) % Mod; for (i = N; i < N * 2 - 1; i++) a[i-N] = c[i] * fact[i-N] % Mod; for (i = N - 1; i < 1048576; i++) a[i] = 0; for (i = 0; i < N - 1; i++) b[i] = fact_inv[N-2-i]; for (i = N - 1; i < 1048576; i++) b[i] = 0; prod_poly_NTT(N - 1, N - 1, a, b, c); for (i = 0; i < N - 1; i++) ans ^= c[i+N-2] * fact_inv[i] % Mod; printf("%lld\n", ans); fflush(stdout); return 0; }