#include <iostream>
#include <iomanip>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <stack>
#include <queue>
#include <bitset>
#include <numeric>
#include <cassert>
#include <random>
#ifdef DEBUG
#include "./Lib/debug.hpp"
#include "./Lib/Timer.hpp"
#include "./Lib/sample.hpp"
#else
#define dump(...)
template<class T>inline auto d_val(T a, T b) { return a; }
#endif

/* (=＾o＾=) */
#define int ll

/* macro */
#define FOR(i, b, e) for(ll i = (ll)(b); i < (ll)(e); ++i)
#define RFOR(i, b, e) for(ll i = (ll)(e-1); i >= (ll)(b); --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define REPC(x,c) for(const auto& x:(c))
#define REPI2(it,b,e) for(auto it = (b); it != (e); ++it)
#define REPI(it,c) REPI2(it, (c).begin(), (c).end())
#define RREPI(it,c) REPI2(it, (c).rbegin(), (c).rend())
#define REPI_ERACE2(it, b, e) for(auto it = (b); it != (e);)
#define REPI_ERACE(it, c) REPI_ERACE2(it, (c).begin(), (c).end())
#define ALL(x) (x).begin(),(x).end()
#define cauto const auto&
/* macro func */
#define SORT(x) do{sort(ALL(x));}while(false)
#define RSORT(x) do{sort((x).rbegin(),(x).rend());}while(false)
#define UNIQUE(v) do{v.erase( unique(v.begin(), v.end()), v.end() );}while(false)
#define MAX(x,y) do{x = std::max(x,y);}while(false)
#define MIN(x,y) do{x = std::min(x,y);}while(false)
#define BR do{cout<<"\n";}while(false)

/* type define */
using ll = long long;
using PAIR = std::pair<ll, ll>;
using VS = std::vector<std::string>;
using VL = std::vector<long long>;
using VVL = std::vector<VL>;
using VVVL = std::vector<VVL>;
using VD = std::vector<double>;
template<class T>
using V = std::vector<T>;

/* using std */
using std::cout;
constexpr char endl = '\n';
using std::cin;
using std::sort;
using std::pair;
using std::string;
using std::stack;
using std::queue;
using std::vector;
using std::list;
using std::map;
using std::unordered_map;
using std::multimap;
using std::unordered_multimap;
using std::set;
using std::unordered_set;
using std::unordered_multiset;
using std::multiset;
using std::bitset;
using std::priority_queue;

/* constant value */
constexpr ll MOD = 1000000007;
//constexpr ll MOD = 998244353;

/* Initial processing  */
struct Preprocessing { Preprocessing() { std::cin.tie(0); std::ios::sync_with_stdio(0); }; }_Preprocessing;

/* Remove the source of the bug */
signed pow(signed, signed) { assert(false); return -1; }

/* define hash */
namespace std { template <>	class hash<std::pair<ll, ll>> { public:	size_t operator()(const std::pair<ll, ll>& x) const { return hash<ll>()(1000000000 * x.first + x.second); } }; }

/* input */
template<class T> std::istream& operator >> (std::istream& is, vector<T>& vec) { for (T& x : vec) is >> x; return is; }

//=============================================================================================

auto solve_correct(const list<PAIR>& data) {

	list<ll> p;
	REPC(tt, data) {
		REP(i, tt.second) { p.emplace_back(tt.first); }
	}
	ll ans = 0;
	ll now = *p.begin();
	REPI2(itr, (++p.begin()), p.end()) {
		now += *itr;
		++ans;
		if (now >= 10) {
			now = 1 + (now % 10);
			++ans;
		}
	}
	return ans;
}

auto solve(ll d, ll c, const V<V<PAIR>>& v) {

	ll cnt = v[d][c % 10].first;
	ll ans = v[d][c % 10].second;

	auto num = (c / 10);
	if (num == 0) { return PAIR{cnt,ans}; }
	cnt += num * (9 + d);

	auto p = solve(d, num, v);
	cnt += p.first;

	if (c % 10 > 0) {
		++cnt;
		ans += p.second;
		if (ans >= 10) {
			++cnt;
			ans = 1 + ans % 10;
		}
	} else {
		ans = p.second;
	}
	//dump(d, c, cnt, ans); BR;
	return PAIR{cnt,ans};
}

auto solve_p(ll m, const list<PAIR>& data) {

	V<V<PAIR>> v(10, V<PAIR>(10));
	REP(n, 10) {
		ll now = n;
		ll cnt = 0;
		v[n][0] = {0,0};
		v[n][1] = {0,now};
		FOR(t, 2, 10) {
			now += n;
			++cnt;
			if (now >= 10) { now = 1 + now % 10; ++cnt; }
			v[n][t] = {cnt,now};
		}
	}

	list<ll> lst;
	ll ans = 0;
	REPC(tt, data) {
		ll d = tt.first;
		ll  c = tt.second;
		auto p = solve(d, c, v);
		//dump(p);
		ans += p.first;
		lst.emplace_back(p.second);
	}

	ll now = *lst.begin();
	REPI2(itr, (++lst.begin()), lst.end()) {
		now += *itr;
		++ans;
		if (now >= 10) {
			now = 1 + (now % 10);
			++ans;
		}
	}
	return ans;
}
signed main() {

	ll m;
	/**/
	cin >> m;
	list<PAIR> data;
	REP(i, m) {
		ll d, c;
		cin >> d >> c;
		data.emplace_back(d, c);
	}
	auto ans = solve_p(m, data);
	cout << ans << endl;

	//auto ans_c = solve_correct(data);
	//cout << ans_c << endl;
	/*/

	auto gen = Sample::SampleGenerator(0);
	REP(_, 500) {
		auto [m] = gen.generate(PAIR{5,20});
		list<PAIR> data;
		REP(i, m) {
			auto [d, c] = gen.generate(PAIR{0,9}, PAIR{1,500});
			data.emplace_back(d, c);
		}

		auto ans = solve_p(m, data);
		auto ans_c = solve_correct(data);
		if (ans != ans_c) {
			cout << m << endl;
			REPC(tt, data) {
				cout << tt.first << " " << tt.second << endl;
			}
			cout << ans << " ";
			cout << ans_c << endl;
			break;
		}
	}
	/*//**/
}


Measured memory_bytes: 15872