#include<bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pf push_front
#define LC k<<1
#define RC k<<1|1
#define IO cin.sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define rep(i,a,n) for (int i = a; i < n; i++)
#define repn(i,a,n) for (int i = a; i <= n; i++)
#define per(i,a,n) for (int i = (n) - 1; i >= a; i--)
#define pern(i,a,n) for (int i = n; i >= a; i--)

typedef long long LL;
typedef long double LD;
typedef unsigned long long ull;
typedef pair<int, int> PII;
typedef pair<int, LL> PIL;
typedef pair<LL, int> PLI;
typedef pair<double, double> PDD;
typedef pair<ull, ull> PUU;
typedef pair<LL, LL> PLL;

const int N = 110000;
const int M = 1100000;
const int mod = 1e9+7;
const int inf = (int)1e9;
const LL INF = 1e18;
const double eps = 1e-9;

mt19937_64 Rand((unsigned long long)new char);
#define rand Rand

int w, cnt = 1, f[N], num[N], ans;
vector<PII> g[N];
void work(int x) {
	cin >> f[x] >> num[x];
	repn(i, 1, num[x]) {
		cnt++;
		int cur = cnt;
		work(cnt);
		g[x].pb(mp(cur, f[cur]));
	}
}
int cal(int x) {
	vector<int> tmp;
	int sum = 0;
	for (auto p: g[x]) {
		int y = p.fi, v = p.se;
		int res = cal(y);
		res += v;
		ans += res / w;
		res %= w;
		tmp.pb(res);
		sum += res;
	}
	sort(all(tmp));
	while (sum >= w) {
		sum -= tmp.back();
		tmp.pop_back();
		ans ++;
	}
	return sum;
}
int main() {
	IO;
	cin >> w;
	work(1);
	ans += (cal(1) + f[1] + w - 1) / w;
	cout << ans << endl;
	return 0;
}