#include "bits/stdc++.h"

using namespace std;

using lint = int64_t;

const int N = 100005;
vector<int> g[N];
lint b[N];
int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    lint w;
    cin>>w;
    int n = 1;
    auto create = [&](int p, auto &self) -> void {
        int v = n++;
        g[p].push_back(v);
        lint cur;
        int child;
        cin>>cur>>child;
        b[v] = cur;
        for(int i =0; i<child; i++)
            self(v, self);
    };
    create(0, create);
    // for(int i =0; i<n; i++){
    //     cout<<i<<": \n ";
    //     for(int v : g[i]){
    //         cout<<v<<" ("<<b[v]<<"), ";
    //     }
    //     cout<<"\n";
    // }
    using pii = pair<lint, lint>;
    auto dfs = [&](int u, auto &self) -> pii {
        lint resto = 0, custo = 0;
        if(g[u].empty()){
            resto = b[u] % w;
            custo = b[u] / w;
            //cout<<" "<<u<<" "<<resto<<" "<<custo<<"\n";
            return {resto, custo};
        }
        vector<pii> child;
        child.reserve(g[u].size());
        for(int v : g[u])
            child.push_back(self(v, self));
        
        sort(child.begin(), child.end());
        lint sum_child = 0;
        int big_child = int(child.size()); 
        for(const auto &[r_child, c_child] : child){
            custo += c_child;
            if(sum_child + r_child <= w){
                sum_child += r_child;
                big_child--;
            }
        }
        custo += big_child;
        if(sum_child + b[u] <= w){ // meu pai arruma

           // cout<<" "<<u<<" "<<sum_child + b[u]<<" "<<custo<<"\n";
            return {sum_child + b[u], custo};
        }


        //fix small child
        if(sum_child > 0){
            custo++;
            lint dif = w - sum_child;
            b[u] = max<lint>(0, b[u] - dif);
        }

        resto = b[u] % w;
        custo += b[u] / w;
       // cout<<" "<<u<<" "<<resto<<" "<<custo<<"\n";
        return {resto, custo};
    };
    auto [resto, custo] = dfs(1, dfs);
    if(resto != 0)
        custo++;
    cout<<custo<<"\n";
    return 0;
}