#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 + 1, 0), G(n + 1, 0);
		for(int i = 0; i <= n - 1; ++i){
			res[i] = dfs(E[x][i]);
		}
		int sufsum = 0, suf = 0;
		for(int i = n - 1; i >= 0; --i){
			sufsum += res[i];
			if(sufsum >= W){
				sufsum -= W;
				++suf;
			}
			G[i] = suf + (sufsum > 0);
		}
		
		if(!n){
			ans += (val[x] / W);
			return val[x] % W;
		}
		
		int mi = G[0];
		int sum = 0;
		int pre = 0, presum = 0, pr = 0;
		int mires = 1e9 + 5;
		
//		{
//			cerr << "res\n";
//			for(int i = 0; i <= n - 1; ++i){
//				cerr << res[i] << " ";
//			}
//			cerr << '\n';
//		}
		for(int i = 0; i <= n - 1; ++i){
			while(pr <= n - 1 && pre + (presum > 0) + G[pr] + 1 > G[0]){
				sum += res[pr];
				++pr;
			}
//			cerr << "now " << i << " " << pr << " " << sum << " " << pre << " " << '\n';
			int t = pre + (presum > 0) + G[pr] + 1;
			if(t == G[0] && sum <= W){
				mires = min(mires, sum);
			}
			sum -= res[i];
			presum += res[i];
			if(presum >= W){
				presum -= W;
				++pre;
			}
		}
		ans += G[0] - 1 + (mires + val[x]) / W;
//		cerr << "last " << G[0] << " " << mires << " " << G[0] - 1 + (mires + val[x]) / W << " " << val[x] << '\n';
		return (mires + val[x]) % W;
	};
	
	cout << ans + (dfs(1) > 0);
	return 0;
}