#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template <class T> vector<T> multivector(size_t N,T init){return vector<T>(N,init);}
template <class... T> auto multivector(size_t N,T... t){return vector<decltype(multivector(t...))>(N,multivector(t...));}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max(a,b);}
template <class T> void chmin(T& a, const T b){a=min(a,b);}
void YN(bool flg) {cout << (flg ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << (flg ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << (flg ? "yes" : "no") << endl;}

//Pow_Mod O(log(n))
long long PowMod(long long x, long long n, long long mod) {
    long long res = 1;
    for (; n > 0; n >>= 1, (x *= x) %= mod) if (n & 1) (res *= x) %= mod;
    return res;
}

pair<ll,ll> ch(ll m,ll n){
	string S = to_string(m)+to_string(n);
	ll cnt = 0;
	while(S.size()>1){
		cnt++;
		int a = S.back()-'0';
		S.pop_back();
		int b = S.back()-'0';
		S.pop_back();
		a = a+b;
		string T = to_string(a);
		S += T;
	}
	pair<ll,ll> p = {ll(S[0]-'0'),cnt};
	return p;
}


int main() {
	SPEED
	ll M; cin >> M;
	vector<ll> d(M),c(M);
	for(int i = 0; i < M; ++i){
		cin >> d[i] >> c[i];
	}
	vector<vector<pair<ll,ll>>> calc(10,vector<pair<ll,ll>>(10));
	for(int i = 0; i < 10; ++i){
		for(int j = 0; j < 10; ++j){
			calc[i][j] = ch(i,j);
		}
	}
	string S;
	ll ans = 0;
	for(ll i = 0; i < M; ++i){
		ll m = d[i], n = 0, x = 0, y = 0;
		for(ll j = c[i]; j>0; j /= 2){
			if(j&1){
				auto p = calc[n][m];
				n = p.first;
				y += p.second + x;
			}
			auto p2 = calc[m][m];
			m = p2.first;
			x = p2.second+2*x;
		}
		S.push_back(char(n+'0'));
		ans += y-1;
	}

	ll cnt = 0;
	while(S.size()>1){
		int a = S.back()-'0';
		S.pop_back();
		int b = S.back()-'0';
		S.pop_back();
		a = a+b;
		string T = to_string(a);
		S += T;
		cnt++;
	}
	ans += cnt;
	cout << ans << endl;

    return 0;
}


Measured memory_bytes: 3716