#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;
        cur.push_back(t);
    }
    sort(cur.begin(), cur.end(), cmp);
    int l = 0, r = cur.size() - 1;
    while (l < r)
    {
        while (l < r && cur[l] + cur[r] > m)
            l++;
        if (l < r)
        {
            cur[l] += cur[r], cur[r] = 0;
            if (cur[l] == m)
                ans++, cur[l] = 0;
        }
        r--;
    }
    int minv = 0x3f3f3f3f, cnt = 0;
    for (int i = 0; i < cur.size(); i++)
        if (cur[i])
            cnt++, minv = min(minv, cur[i]);
    if (cnt)
        ans += cnt - 1;
    return w[u] + (cnt ? minv : 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;
}