#include<bits/stdc++.h>
using namespace std ;
typedef long long ll ;
typedef unsigned long long ull ;
typedef pair < int , int > pii ; 
typedef vector<int> vi;
#define fi first
#define se second
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()


const int MAXN = 1e5 + 7 ;

int lim , n ;
vector < pii > v[ MAXN ] ;

pair < int , int > dp[ MAXN ] ;



void dfs ( int x ) {
    vector < int > hh ;
    for ( auto [ y , add ] : v[ x ] ) {
        dfs ( y ) ;
        dp[ x ].fi += dp[ y ].fi ;
        int tot = dp[ y ].se + add ;
        int rem = tot % lim ;
        if ( rem == 0 ) { rem = lim ; }
        hh.push_back ( rem ) ;
        dp[ x ].fi += ( tot - rem ) / lim ;
    }
    sort ( hh.begin ( ) , hh.end ( ) ) ;
    int tot = hh.size ( ) ;
    for ( auto val : hh ) {
        if ( dp[ x ].se + val <= lim ) { 
            dp[ x ].se += val ;
            -- tot ;
        }
    }
    dp[ x ].fi += tot ;
    // printf ( "dp[ %d ] = { %d , %d }\n" , x , dp[ x ].fi , dp[ x ].se ) ;
}

void solve ( ) {
    cin >> lim ;
    stack < pii > s ;
    s.push ( { 1 , 1 } ) ;
    int tp = 1 ;
    while ( s.empty ( ) == false ) {
        auto [ x , cnt ] = s.top ( ) ;
        s.pop ( ) ;
        if ( cnt > 1 ) {
            s.push ( { x , cnt - 1 } ) ;
        }
        int len , foo ;
        cin >> len >> foo ;
        ++ tp ;
        v[ x ].push_back ( { tp , len } ) ;
        // printf ( "edge %d %d %d\n" , x , tp , len ) ;
        if ( foo > 0 ) { 
            s.push ( { tp , foo } ) ;
        }
    }
    dfs ( 1 ) ;
    cout << dp[ 1 ].fi + 1 << "\n" ;
}

int main ( ) {
    ios_base :: sync_with_stdio ( false ) ;
    cin.tie ( NULL ) ;
    int t = 1 ; // cin >> t ; 
    while ( t -- ) { solve ( ) ; }
    return 0 ;
}