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

#define ff   first
#define ss   second
#define pb   push_back

typedef long long   ll;
typedef pair<int,int>   ii;

const int N = 3e5+5;
const int mod = 1e9+7;

vector <ii> g[N];
ii dp[N];
int w;
	
void go (int u) { 
	vector <int> x;
	for (auto &e : g[u]) {
		go(e.ff);
		int v1 = (dp[e.ff].ss + e.ss) / w;
		int v2 = (dp[e.ff].ss + e.ss) % w;
		if ((dp[e.ff].ss + e.ss) % w == 0) v1--, v2 = w;
		dp[u].ff += dp[e.ff].ff + v1;
		x.pb(v2);
	}
	sort (x.begin(), x.end());
	
	int sz = x.size();
	x.pb(mod);
	int curr = 0;
	for (int i = 0; i <= sz; ++i) { 
		curr += x[i];
		if (curr > w) { 
			dp[u].ff += sz - i;
			dp[u].ss = curr - x[i];
			break;
		}
	}
}

int main() { 
	#ifdef LOCAL
	freopen("in.txt","r",stdin);
	#endif
	cin >> w;
	int cur_node = 0;
	stack <ii> st;
	st.push({0, ++cur_node});
	while (st.size()) { 
		int m, n; cin >> m >> n;
		ii tp = st.top();
		st.pop();
		g[tp.ff].pb({tp.ss, m});
		for (int i = 0; i < n; ++i) {
			st.push({tp.ss, ++cur_node});
		}
	}
	go(0);
	cout << dp[0].ff + 1 << '\n';
	return 0;
}