#include <bits/stdc++.h>
using namespace std;

// エイリアス
using  ll = long signed long;
using ull = long unsigned long;
using  ld = long double;
using   P = pair<int, int>;
using llP = pair<ll, ll>;
using DoP = pair<double, double>;

// 汎用マクロ
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define FOREACH(i,q) for (auto &i : q)
#define UNIQUE(v) do { sort((v).begin(), (v).end()); (v).erase(unique((v).begin(), (v).end()), (v).end()); } while (false)
#define SZ(x) ((int)(x).size())
template <class T>inline bool chmin(T &a, const T b) {if (a > b) { a = b; return true;} return false;}
template <class T>inline bool chmax(T &a, const T b) {if (a < b) { a = b; return true;} return false;}
template <class T>inline void line_out(const vector<T> vec) {int n = SZ(vec); rep(i, n) { cout << vec[i]; if(i < n-1) cout << " ";}cout << endl;}
const int di[] = {0, 1, 0, -1, 1, 1, -1, -1};
const int dj[] = {1, 0, -1, 0, 1, -1, 1, -1};
const int INF = 1 << 28;
const ll INF64 = 1ll << 60;
const int mod = 1000000007;
//const int mod = 998244353;
struct mint
{
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a)
  {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a)
  {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a)
  {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const
  {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const
  {
    mint res(*this);
    return res -= a;
  }
  mint &operator++()
  {
    if ((x += 1) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator--()
  {
    if ((x += mod - 1) >= mod)
      x -= mod;
    return *this;
  }
  mint operator*(const mint a) const
  {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const
  {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const
  {
    return pow(mod - 2);
  }
  mint &operator/=(const mint a)
  {
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const
  {
    mint res(*this);
    return res /= a;
  }
};



int main()
{
  int m; cin >> m;
  vector<vector<llP>> table(10, vector<llP>(52)); //count, result
  rep(i, 10) table[i][0] = make_pair(0, i);
  rep(i, 10) {
    for(int k = 1; k < 51; ++k) {
      ll count, result;
      result = table[i][k-1].second*2;
      if(result < 10) {
        count = table[i][k-1].first*2+1;
      }
      else {
        result = result/10 + result%10;
        count = table[i][k-1].first*2+2;
      }
      table[i][k] = make_pair(count, result);
    }
  }
  ll ans = 0;
  string s;
  rep(i, m) {
    ll d, c;
    cin >> d >> c;
    for(int k = 51; k >= 0; --k) {
      if(c >= (1ll<<k)) {
        c -= (1ll<<k);
        ans += table[d][k].first;
        s += char(table[d][k].second + '0');
      }
    }
  }
  reverse(ALL(s));

  while(s.size() > 1) {
    int x = s.back()-'0'; s.pop_back();
    int y = s.back()-'0'; s.pop_back();
    int z = x+y;
    ++ans;
    if(z >= 10) {
      ++ans;
      z = z/10 + z%10;
    }
    s.push_back(z+'0');
  }
  cout << ans << endl;
}


Measured memory_bytes: 7072