#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int MAXN = 310;
const int MOD = 1e9 + 7;

ll _pow(ll a, ll x) {
	ll r = 1;
	while (x) {
		if (x & 1) r = r * a % MOD;
		a = a * a % MOD;
		x /= 2;
	}
	return r;
}

int n, a[MAXN], sub[MAXN];
vector<int> b;
vector<int> g[MAXN];

ll inv[MAXN];
ll dp[MAXN][MAXN][MAXN];
ll tmp[MAXN][MAXN];
void dfs(int v) {
	for (int i = 1; i <= a[v]; i++) {
		dp[v][i][1] = (b[i] - b[i - 1]) * _pow(b[a[v]], MOD - 2) % MOD;
	}
	sub[v] = 1;
	for (int x : g[v]) {
		dfs(x);
		for (int s = 0; s <= sub[v]; s++) {
			for (int t = 0; t <= sub[x]; t++) {
				for (int i = 1; i <= a[v]; i++) {
					tmp[i][s + t] = (tmp[i][s + t] + dp[v][i][s] * dp[x][i][t]) % MOD;
				}
			}
		}
		sub[v] += sub[x];
		for (int i = 1; i <= a[v]; i++) {
			for (int j = 0; j <= sub[v]; j++) {
				dp[v][i][j] = tmp[i][j];
				tmp[i][j] = 0;
			}
		}
	}
	for (int i = 1; i <= a[v]; i++) {
		for (int j = 1; j <= sub[v]; j++) {
			dp[v][i][j] = dp[v][i][j] * inv[j] % MOD;
		}
	}
	for (int i = (int)b.size(); i >= 0; i--) {
		dp[v][i][0] = dp[v][i + 1][0];
		for (int j = 1; j <= sub[v]; j++)
			dp[v][i][0] = (dp[v][i][0] + dp[v][i + 1][j]) % MOD;
	}
}
int main() {
	cin.tie(0); ios_base::sync_with_stdio(0);
	for (int i = 1; i < MAXN; i++) 
		inv[i] = _pow(i, MOD - 2);
	cin >> n;
	int r = -1;
	for (int i = 1; i <= n; i++) {
		int x, p; cin >> x >> p;
		if (p == 0)
			r = i;
		else
			g[p].push_back(i);
		a[i] = x;
		b.push_back(x);
	}
	b.push_back(0);
	sort(b.begin(), b.end());
	b.erase(unique(b.begin(), b.end()), b.end());
	for (int i = 1; i <= n; i++) {
		a[i] = lower_bound(b.begin(), b.end(), a[i]) - b.begin();
	}
	dfs(r);
	cout << dp[r][0][0];
}