/* 
 Author:N_o_o_B 
 Created:November 23 2019 18:06:10
*/
#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define TRACE
#ifdef TRACE
#define trace(...) { cerr<<"[ "; __trace__(#__VA_ARGS__, __VA_ARGS__);}
#undef endl
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const pair<Arg1,Arg2> &x) {
    return out<<"("<<x.first<<","<<x.second<<")";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const vector<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const set<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const map<Arg1,Arg2> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1>
void __trace__(const string name, Arg1&& arg1){
    cerr << name << " : " << arg1 << " ] " << endl;
}
 
template <typename Arg1, typename... Args>
void __trace__(const string names, Arg1&& arg1, Args&&... args){
    const string name = names.substr(0,names.find(','));
    cerr<<name<<" : "<<arg1<<" | ";
    __trace__(names.substr(1+(int)name.size()), args...);
}
#else
    #define trace(args...)
#endif
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pair<int,int>> vii;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<pair<ll,ll>> vll;
typedef vector<vl> vvl;
typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> oset;
#define fori(i,n) for(int i=0;i<n;i++)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repd(i,a,b) for(int i=a;i>=b;i--)
#define ford(i,n)  for(int i=n-1;i>=0;i--)
#define all(x) x.begin(),x.end()
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define fi first
#define se second
clock_t time_p=clock();
void time_taken()
{
    time_p=clock()-time_p;
    cerr<<"Time Taken : "<<(float)(time_p)/CLOCKS_PER_SEC<<"\n";
}
//const ll mod=998244353;
const ll mod=1e9+7;
const ll INF=1e18;
pair<ll,ll> g(ll num){
    if(num==0) return {0,1};
    ll cnt=0;
    while(num>9){
        ll a=num/10,b=num%10;
        num=a+b;
        cnt++;
    }
    return {num,cnt};
}
pair<ll,ll> f(ll x,ll n){
    if(n==1) return {x,0};
    if(n==2){
        if(x==0) return {0,1};
        if(x==1) return {2,1};
        if(x==2) return {4,1};
        if(x==3) return {6,1};
        if(x==4) return {8,1};
        if(x==5) return {1,2};
        if(x==6) return {3,2};
        if(x==7) return {5,2};
        if(x==8) return {7,2};
        if(x==9) return {9,2};
    }
    auto foo=f(x,2);
    ll cnt = n/2*foo.se;
    auto p1=f(foo.fi,n/2);
    cnt+=p1.se;
    if(n%2==0) return {p1.fi,cnt};
    ll num=p1.fi*10+x;
    auto bar = g(num);
    num=bar.fi;cnt+=bar.se;
    return {num,cnt};
}
void solve(vl a,ll ans){
    ll n=sz(a);
    for(ll i=0;i<n-1;i++){
        auto p=g(a[i]*10+a[i+1]);
        ans += p.se;
        a[i+1]=p.fi;
    }
    cout << ans << endl;
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
    cout.precision(12);cout << fixed;
    int m;
    cin >> m;
    vl a;
    ll ans=0;
    fori(i,m){
        ll d,c;
        cin >> d >> c;
        auto p=f(d,c);
        //trace(d,c,p);
        ans+=p.se;
        a.pb(p.fi);
    }
    solve(a,ans);

    time_taken();
    return 0;
}

Measured memory_bytes: 3568