#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <climits>
#include <cstring>

#define rep(i, m, n) for(int i=int(m);i<int(n);i++)
#define all(c) begin(c),end(c)

template<typename T1, typename T2>
inline void chmin(T1 &a, T2 b) { if (a > b) a = b; }

template<typename T1, typename T2>
inline void chmax(T1 &a, T2 b) { if (a < b) a = b; }

typedef long long int ll;
using ll = long long int;
using ull = long long unsigned int;
using Int = long long int;
using namespace std;
#define INF (1 << 30) - 1
#define INFl (ll)5e15
#define DEBUG 0
#define dump(x)  cerr << #x << " = " << (x) << endl
#define MOD 1000000007


//edit
class Solve {
public:
    Int M;
    vector<pair<Int, Int> > dc;

    Int conv(Int x) {
        int ret = 2 * x;
        if (ret > 0) ret -= 9;
        return ret;
    }

    void solve() {
        cin >> M;
//        dc.resize(M);

        Int ans = 0ll;
        for (int i = 0; i < M; ++i) {
            Int d, c;
            cin >> d >> c;
            if (d == 0) {
                ans += c;
            } else {
                dc.emplace_back(d, c);
//                cin >> dc[i].first >> dc[i].second;
            }

        }

        while (true) {
            vector<pair<Int, Int>> ndc;
            bool flag = false;
            for (auto e : dc) {
                if (e.second > 1) flag = true;
                if (e.first < 5) {
                    if (e.second >= 2)
                        ndc.emplace_back(e.first * 2, e.second / 2);
                    ans += e.second / 2;
                    if (e.second % 2)
                        ndc.emplace_back(e.first, 1);
                } else {
                    if (e.second >= 2)
                        ndc.emplace_back(e.first * 2 - 9, e.second / 2);
                    ans += (e.second / 2) * 2;
                    if (e.second % 2)
                        ndc.emplace_back(e.first, 1);
                }
            }
            dc = ndc;
            if (!flag) {
                break;
            }
        }

        vector<Int> vec;
        for (auto e : dc) {
            vec.push_back(e.first);
        }

        while (vec.size() > 1) {
            Int l = *(vec.end() - 2);
            Int r = *(vec.end() - 1);
            vec.pop_back();
            vec.pop_back();

            if (l + r >= 10) {
                vec.push_back(l + r - 9);
                ans += 2;
            } else {
                vec.push_back(l + r);
                ans++;
            }

        }

        cout << ans << endl;


    }
};


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    Solve().solve();


    return 0;
}


Measured memory_bytes: 145824