#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <vector>
using namespace std;
typedef long long LL;
const int N = 1e5 + 10;
int n, m, w[N];
vector<int> e[N];
int ans;
bool cmp(int a, int b)
{
    return a > b;
}
void dfs(int u)
{
    int k;
    cin >> w[u] >> k;
    for (int i = 1; i <= k; i++)
        e[u].push_back(n + 1), dfs(++n);
}
int dfs2(int u)
{
    vector<int> cur;
    for (int i = 0; i < e[u].size(); i++)
    {
        int j = e[u][i];
        int t = dfs2(j);
        ans += t / m;
        t %= m;
        if (t)
            cur.push_back(t);
    }
    sort(cur.begin(), cur.end());
    int sum = 0;
    for (int i = 0; i < cur.size(); i++)
        sum += cur[i];
    if (sum <= m)
        return w[u] + sum;
    if (cur.size())
        ans += cur.size() - 1;
    // cout << ':' << w[u] + (cur.size()>0 ? cur[0] : 0) << ' ' << cnt << ' ' << ans << endl;
    return w[u] + (cur.size() > 0 ? cur[0] : 0);
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> m;
    dfs(++n);
    int t = dfs2(1);
    ans += (t - 1) / m + 1;
    cout << ans << endl;
    return 0;
}