#include <bits/stdc++.h>

#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx_ori[4] = { -1,0, 1,0 }, dy_ori[4] = { 0,1,0,-1 };
int dx[4] = {0, 0, 0, 0}, dy[4] = {0, 0, 0, 0};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
// #define mp make_pair
//#define endl '\n'

struct dice {
  mt19937 mt;
  dice() : mt(chrono::steady_clock::now().time_since_epoch().count()) {}
  // [0, x)の一様乱数
  ll operator()(ll x) { return this->operator()(0, x); }
  // [x, y)の一様乱数
  ll operator()(ll x, ll y) {
    uniform_int_distribution<ll> dist(x, y - 1);
    return dist(mt);
  }
  vl operator()(int n, ll x, ll y) {
    vl res(n);
    for (int i = 0; i < n; i++) res[i] = this->operator()(x, y);
    return res;
  }
} rnd;

ll dfs(string x) {
  if (x.size() == 1) return 1;
  int n = x.size();
  vl res;
  rep (i, n - 1) {
    int add = (x[i] - '0') + (x[i + 1] - '0');
    string nex = x.substr(0, i) + to_string(add) + x.substr(i + 2, n - 1 - (i + 1));
    res.push_back(dfs(nex));
  }
  sort(all(res));
  assert(res[0] == res.back());
  return res.back() + 1;
}


vi nokori;
ll solve(int d, int k) {
  if (k == 0) return 0;
  ll res = 0;
  if (k % 2 == 1) {
    nokori.push_back(d);
    k--;
  }
  if (d <= 4) {
    res += k / 2;
    res += solve(d * 2, k / 2);
  }
  else {
    res += k;
    res += solve((d - 5) * 2 + 1, k / 2);
  }
  return res;
}

signed main() {
  int m;
  cin >> m;
  ll ans = 0;
  rep (i, m) {
    int d, c;
    cin >> d >> c;
    ans += solve(d, c);
  }
  //DEBUG(ans);
  //DEBUG_VEC(nokori);
  int now = nokori[0];
  for (int i = 1; i < nokori.size(); i++) {
    now = now + nokori[i];
    ans++;
    while (now >= 10) {
      now = now % 10 + 1;
      ans++;
    }
  }
  cout << ans << endl;
  return 0;
  
  map<int, int> mp;
  while (true) {
    ll x = rnd(100000);
    string s = to_string(x);
    DEBUG(x);
    DEBUG(dfs(s));
  }
}


Measured memory_bytes: 35172