#include<bits/stdc++.h>
#define pb emplace_back

using namespace std;
using LL = long long;



int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int W;
	cin >> W;
	const int maxn = 1e6 + 5;
	int cur = 0;
	vector<int> E[maxn], val(maxn, 0);
	
	function<void(int)> read_tree = [&](int x){
		int sz;
		cin >> val[x] >> sz;
		for(int i = 1; i <= sz; ++i){
			++cur;
			E[x].pb(cur);
			read_tree(cur);
		} 	
	};
	
	read_tree(++cur);
	
	int ans = 0;
	
	function<int(int)> dfs = [&](int x){
		int n = E[x].size();
		vector<int> res(n, 0);
		for(int i = 0; i <= n - 1; ++i){
			res[i] = dfs(E[x][i]);
		}
		sort(res.begin(), res.end());
		int mi = n, mires = 0;
		int sum = 0;
		for(int i = 0; i <= n; ++i){
			if(sum > W){
				break;
			}
			if(mi > (n - i)){
				mi = (n - i);
				mires = sum;
			}
			else if(mi == (n - i) && sum < mires){
				mires = sum;
			}
			if(i != n)
				sum += res[i];
		}
		ans += mi + (mires + val[x]) / W;
//		{
//			for(int i = 0; i <= n - 1;++i)
//				cerr <<res[i] << " ";
//			cerr << '\n'; 
//		}
//		cerr << "last " << val[x] << " " << mi << " " << mires << '\n';
		return (mires + val[x]) % W;
	};
	
	cout << ans + (dfs(1) > 0);
	return 0;
}