#include<bits/stdc++.h>
using namespace std;
#define cs const
#define re register
#define pb push_back
#define pii pair<int,int>
#define ll long long
#define y1 shinkle
#define fi first
#define se second
#define bg begin
namespace IO{

cs int RLEN=1<<22|1;
#define gc getchar
inline int read(){
    char ch=gc();
    int res=0;bool f=1;
    while(!isdigit(ch))f^=ch=='-',ch=gc();
    while(isdigit(ch))res=(res*10)+(ch^48),ch=gc();
    return f?res:-res;
}
inline ll readll(){
    char ch=gc();
    ll res=0;bool f=1;
    while(!isdigit(ch))f^=ch=='-',ch=gc();
    while(isdigit(ch))res=(res*10)+(ch^48),ch=gc();
    return f?res:-res;
}
inline char readchar(){
	char ch=gc();
	while(isspace(ch))ch=gc();
	return ch;
}
inline int readstring(char *s){
	int top=0;char ch=gc();
	while(isspace(ch))ch=gc();
	while(!isspace(ch)&&ch!=EOF)s[++top]=ch,ch=gc();
	s[top+1]='\0';return top;
}

}
using IO::read;
using IO::readll;
using IO::readchar;
using IO::readstring;
template<typename tp>inline void chemx(tp &a,tp b){(a<b)?(a=b):0;}
template<typename tp>inline void chemn(tp &a,tp b){(a>b)?(a=b):0;}


cs int N=100005;

int n,w[N],W;
vector<int> e[N];

ll ans;

int dfs(int u){
    int sm=0;
    vector<int>son;
    for(int v:e[u]){
        int x=dfs(v);
        if(x>0)
        son.pb(x);
        sm+=x;
    }
    sort(son.begin(),son.end());
    if(sm>W){
        sm=0;
        for(int i=0;i<son.size();i++){
            if(sm+son[i]>W){
                ans+=son.size()-i;
                break;
            }
            sm+=son[i];
        }
    }
    sm+=w[u];
    if(sm>=W)ans+=sm/W,sm%=W;
    return sm;
}

void getin(int fa,int sz){
    for(int i=1;i<=sz;i++){
        n++;
        e[fa].pb(n);
        w[n]=read();int siz=read();
        if(siz)getin(n,siz);
    }
}

int main(){
    W=read();
    n=1;
    getin(n,1);
    int x=dfs(1);
    if(x)ans++;
    cout<<ans<<'\n';
}