#include <iostream>
#include <vector>
#include <cstdio>

using namespace std;

int W[20005];
int T[20005];
vector<int> sons[20005];
int cnt = 0;
int dp[20005][700];
int ch[20005];
int s;

void input(int fa){
    int tt = cnt;
    cnt++;
    int a,b;
    cin >> a >> b;
    if(fa!=-1){
        sons[fa].push_back(tt);
    }
    a*=2;
    if(b!=0) ch[tt] = 1;
    T[tt] = a;
    W[tt] = b;
    if(b==0){
        input(tt);
        input(tt);
    }
}

void print(int x){
    if(sons[x].size()>=1) print(sons[x][0]);
    cout << T[x] << endl;
    if(sons[x].size()>=2) print(sons[x][1]);
}

void dfs(int x){
    if(ch[x]){
        for(int i = 0; i<=s-T[x]; i++){
            dp[x][i+T[x]] = (i/5 <= W[x])? i/5 : W[x];
        }
        return;
    }
    for(int i = 0; i<sons[x].size(); i++){
        int y = sons[x][i];
        dfs(y);
        for(int j = s; j>=T[y]; j--){
            for(int k = 0; k<=j-T[y]; k++)
                dp[x][j] = max(dp[x][j], dp[x][j-k] + dp[y][k]);
        }
    }
}

int main() {
    cin >> s;
    s--;
    input(-1);
    dfs(0);
    cout << dp[0][s] << endl;
    return 0;
}