1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
#include <bits/stdc++.h>
using namespace std;
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
	*this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
// debug & operator << (debug & dd, P p) { dd << "(" << p.x << ", " << p.y << ")"; return dd; }

const int nax = 1e6 + 5;
#define left left_compile
#define right right_compile
int left[nax], right[nax];
int subtree[nax];

long long dfs(int a, int b, int pref, int suf) {
	assert(pref == 0 || suf == 0);
	if(a == 0 && b == 0) {
		return 0;
	}
	long long my_value = 0;
	debug() << imie(a) imie(b) imie(pref) imie(suf);
	for(int rep = 0; rep < 2; ++rep) {
		if(b == 0) {
			assert(pref || suf);
			my_value += dfs(left[a], 0, 0, subtree[left[a]]);
			my_value += dfs(right[a], 0, subtree[right[a]], 0);
			if(pref) {
				my_value += subtree[left[a]];
			}
			else {
				my_value += subtree[right[a]];
			}
			debug() << "a" imie(a) imie(b) imie(pref) imie(suf) imie(my_value);
			return my_value;
		}
		swap(a, b);
	}
	assert(a > 0 && b > 0);
	for(int rep = 0; rep < 2; ++rep) {
		if(subtree[a] > subtree[b] && pref >= 1 + subtree[left[a]]) {
			my_value += subtree[left[a]];
			my_value += dfs(right[a], b, pref - (1+subtree[left[a]]), 0);
			my_value += dfs(left[a], 0, 0, subtree[left[a]]);
			debug() << "b" imie(a) imie(b) imie(pref) imie(suf) imie(my_value);
			return my_value;
		}
		// if(left[a] == 0 && subtree[a] == subtree[b]) {
			// assert(pref == 0 && suf == 0);
			// dfs(right[a], b, 1, 0);
			// return;
		// }
		if(subtree[a] > subtree[b] && suf >= 1 + subtree[right[a]]) {
			my_value += subtree[right[a]];
			my_value += dfs(left[a], b, 0, suf - (1+subtree[right[a]]));
			my_value += dfs(right[a], 0, subtree[right[a]], 0);
			// dfs(left[a], b, 0, suf - 1);
			debug() << "c" imie(a) imie(b) imie(pref) imie(suf) imie(my_value);
			return my_value;
		}
		// if(right[a] == 0 && subtree[a] == subtree[b]) {
			// assert(pref == 0 && suf == 0);
			// dfs(left[a], b, 0, 1);
		// }
		swap(a, b);
	}
	
	if(pref == 0 && suf == 0) {
		my_value += abs(subtree[left[a]] - subtree[left[b]]);
	}
	if(pref == 0) {
		my_value += dfs(left[a], left[b], 0, abs(subtree[left[a]] - subtree[left[b]]));
	}
	else {
		my_value += subtree[left[a]] + subtree[left[b]];
		my_value += dfs(left[a], 0, 0, subtree[left[a]]);
		my_value += dfs(0, left[b], 0, subtree[left[b]]);
	}
	if(suf == 0) {
		my_value += dfs(right[a], right[b], abs(subtree[right[a]] - subtree[right[b]]), 0);
	}
	else {
		// debug() << imie(answer) imie(a) imie(b);
		my_value += subtree[right[a]] + subtree[right[b]];
		// debug() << imie(answer);
		my_value += dfs(right[a], 0, subtree[right[a]], 0);
		my_value += dfs(0, right[b], subtree[right[b]], 0);
	}
	debug() << "d" imie(a) imie(b) imie(pref) imie(suf) imie(my_value);
	return my_value;
}

void dfs_subtree(int a) {
	subtree[a] = 1;
	for(int b : {left[a], right[a]}) {
		if(b != 0) {
			dfs_subtree(b);
			subtree[a] += subtree[b];
		}
	}
}

int main() {
	int n;
	scanf("%d", &n);
	int root[2] = {-1, -1};
	for(int rep = 0; rep < 2; ++rep) {
		int add = rep * n;
		for(int i = 1; i <= n; ++i) {
			int par;
			scanf("%d", &par);
			if(par == -1) {
				root[rep] = i+add;
			}
			else {
				if(i < par) {
					left[par+add] = i+add;
				}
				else {
					right[par+add] = i+add;
				}
			}
		}
	}
	dfs_subtree(root[0]);
	dfs_subtree(root[1]);
	debug() << range(subtree + 1, subtree + n + 1);
	debug() << range(subtree + n + 1, subtree + 2 * n + 1);
	long long answer = dfs(root[0], root[1], 0, 0);
	printf("%lld\n", answer % 1'000'000'007);
}