#include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <complex>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <iterator>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <regex>
#include <limits>
#include <time.h>
#include <cstdint>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define sc second
#define fr first
#define stpr setprecision
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define rep(i,n) for(ll i=0;i<(n);++i)
#define Rep(i,a,b) for(ll i=(a);i<(b);++i)
#define rrep(i,n) for(ll i=n-1;i>=0;i--)
#define rRep(i,a,b) for(ll i=a;i>=b;i--)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
ll gcd(ll a,ll b){return (b == 0 ? a : gcd(b, a%b));}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ll INF=1000000011;
constexpr ll MOD2=998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS=10e-8;
template <class T, class U> inline bool chmax(T& lhs, const U& rhs) { if (lhs < rhs) { lhs = rhs; return 1; } return 0; }
template <class T, class U> inline bool chmin(T& lhs, const U& rhs) { if (lhs > rhs) { lhs = rhs; return 1; } return 0; }
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
  for(auto i=begin(v); i != end(v); ++i){
    if(i !=begin(v)) os << ' ';
    os << *i;
  }
  return os;
}

ll RMQ(ll a,ll b){
  return min(a,b);
}

template <typename T>
struct SegmentTree{
  using F = function<T(T,T)>;
  int n;
  F f;
  T ti;
  vector<T> dat;
  SegmentTree(){};
  SegmentTree(F f,T ti):f(f),ti(ti){}
  void init(int n_){    
    n=1;
    while(n<n_){
      n<<=1;
    }
    dat.assign(n<<1,ti);
  }
  void build(const vector<T> &v){
    int n_=v.size();
    init(n_);
    for(int i=0;i<n_;i++){
      dat[n+i]=v[i];
    }
    for(int i=n-1;i;i--){
      dat[i]=f(dat[(i<<1)|0],dat[(i<<1)|1]);
    }
  }
  void set_val(int k,T x){
    dat[k+=n]=x;
    while(k>>=1){
      dat[k]=f(dat[(k<<1)|0],dat[(k<<1)|1]);    
    }
  }
  T query(int a,int b){
    T vl=ti,vr=ti;
    for(int l=a+n,r=b+n;l<r;l>>=1,r>>=1) {
      if(l&1){
        vl=f(vl,dat[l++]);
      }
      if(r&1){
        vr=f(dat[--r],vr);
      }
    }
    return f(vl,vr);
  }
};

ll  A[200007],B[200007];
ll keta,wa;
int main(){
  ll M;
  cin  >> M;
  rep(i,M){
    cin >> A[i] >> B[i];
    keta+=B[i];
    wa+=A[i]*B[i];
  }
  cout << keta-1+wa/9+(wa%9==0 ? -1 :0)  << endl;
}


Measured memory_bytes: 6672