//#define NDEBUG
#include "bits/stdc++.h"
#include <iostream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <array>
#ifdef _MSC_VER
#include <ppl.h>
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#endif

using namespace std;

#define DUMPOUT cerr
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

typedef unsigned uint; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<double, double> pdd; typedef pair<string, string> pss;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const pair<_KTy, _Ty>& m) { o << "{" << m.first << ", " << m.second << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const unordered_map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const vector<_Ty>& v) { if (v.empty()) { o << "{ }"; return o; } o << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const unordered_set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; }	o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const stack<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } stack<_Ty> t(s); o << "{" << t.top(); t.pop(); while (!t.empty()) { o << ", " << t.top(); t.pop(); } o << "}";	return o; }
template <typename _Ty> ostream& operator << (ostream& o, const list<_Ty>& l) { if (l.empty()) { o << "{ }"; return o; } o << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& is, pair<_KTy, _Ty>& m) { is >> m.first >> m.second; return is; }
template <typename _Ty> istream& operator >> (istream& is, vector<_Ty>& v) { for (size_t t = 0; t < v.size(); t++) is >> v[t]; return is; }
namespace aux { // print tuple
  template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
  template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& v) { os << get<N>(v); } };
}

template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); }

#define PI 3.14159265358979323846
#define EPS 1e-8
#define FOR(t,a,n) for(int t=(a);t<(n);++t)
#define REP(t,n)  FOR(t,0,n)
#define all(j) (j).begin(), (j).end()
#define SZ(j) ((int)(j).size())
#define fake false

class Timer {
public:
  double t = 0;
  Timer() {}
  static double time() {
#ifdef _MSC_VER
    return __rdtsc() / 2.8e9;
#else
    unsigned long long a, d;
    __asm__ volatile("rdtsc"
      : "=a"(a), "=d"(d));
    return (d << 32 | a) / 2.8e9;
#endif
  }
  void measure() { t = time() - t; }
  double elapsedMs() { return (time() - t) * 1000.0; }
} timer;

struct Xorshift {
  uint64_t x = 88172645463325252LL;
  unsigned nextUInt() {
    x = x ^ (x << 7);
    return x = x ^ (x >> 9);
  }
  unsigned nextUInt(unsigned mod) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % mod;
  }
  unsigned nextUInt(unsigned l, unsigned r) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % (r - l + 1) + l;
  }
  double nextDouble() {
    return double(nextUInt()) / UINT_MAX;
  }
};

template<typename T>
void shuffleVector(vector<T>& v, Xorshift& rnd) {
  int n = v.size();
  for (int t = n - 1; t >= 1; t--) {
    int r = rnd.nextUInt(t);
    swap(v[t], v[r]);
  }
}



void rec(vector<int> v, int depth = 0) {
  if (v.size() == 1) {
    cerr << depth << ": " << v << endl;
    return;
  }
  for (int i = 0; i < (int)v.size() - 1; i++) {
    int s = v[i] + v[i + 1];
    vector<int> nv(v);
    if (s >= 10) {
      nv[i] = s / 10;
      nv[i + 1] = s % 10;
    }
    else {
      for (int j = i; j < (int)nv.size() - 1; j++) {
        nv[j] = nv[j + 1];
      }
      nv.pop_back();
      nv[i] = s;
    }
    rec(nv, depth + 1);
  }
}



// n が k 個ある状態から r ラウンドで n が 1 個の状態になる
int ks[10], rs[10];
void repete(int n) {
  int x = n;
  int k = 1;
  int r = 0;
  do {
    if (x >= 10) {
      x = x / 10 + x % 10;
      r++;
    }
    else {
      x += n;
      k++;
      r++;
    }
  } while (x != n);
  ks[n] = k; rs[n] = r;
}

struct S {
  int n;
  ll k, r;
  S(int d, ll c) : n(d), k(c), r(0) {}
  void build() {
    ll a = (k - 1) / (ks[n] - 1);
    k = k - a * (ks[n] - 1);
    r = r + a * rs[n];
  }
};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  for (ll i = 0; i <= 9; i++) repete(i);

  int M;
  cin >> M;

  ll ans = 0;

  vector<int> ds;
  for (int i = 0; i < M; i++) {
    int d;
    ll c;
    cin >> d >> c;
    S s(d, c);
    s.build();
    ans += s.r;
    for (ll i = 0; i < s.k; i++)
      ds.push_back(s.n);
  }

  while (ds.size() > 1) {
    int n = ds.size();
    int x = ds[n - 2] + ds[n - 1];
    if (x >= 10) {
      ds[n - 2] = x / 10;
      ds[n - 1] = x % 10;
    }
    else {
      ds[n - 2] = x;
      ds.pop_back();
    }
    ans++;
  }

  cout << ans << endl;

  return 0;
}

Measured memory_bytes: 6384