Problem:
Score: 500 points

Problem Statement

N programmers are going to participate in the preliminary stage of DDCC 20XX. Due to the size of the venue, however, at most 9 contestants can participate in the finals.

The preliminary stage consists of several rounds, which will take place as follows:

All the N contestants will participate in the first round.

When X contestants participate in some round, the number of contestants advancing to the next round will be decided as follows:

The organizer will choose two consecutive digits in the decimal notation of X, and replace them with the sum of these digits. The number resulted will be the number of contestants advancing to the next round.

For example, when X = 2378, the number of contestants advancing to the next round will be 578 (if 2 and 3 are chosen), 2108 (if 3 and 7 are chosen), or 2315 (if 7 and 8 are chosen).

When X = 100, the number of contestants advancing to the next round will be 10, no matter which two digits are chosen.

The preliminary stage ends when 9 or fewer contestants remain.

Ringo, the chief organizer, wants to hold as many rounds as possible.
Find the maximum possible number of rounds in the preliminary stage.

Since the number of contestants, N, can be enormous, it is given to you as two integer sequences d_1, \ldots, d_M and c_1, \ldots, c_M, which means the following: the decimal notation of N consists of c_1 + c_2 + \ldots + c_M digits, whose first c_1 digits are all d_1, the following c_2 digits are all d_2, \ldots, and the last c_M digits are all d_M.

Constraints

1 \leq M \leq 200000

0 \leq d_i \leq 9

d_1 \neq 0

d_i \neq d_{i+1}

c_i \geq 1

2 \leq c_1 + \ldots + c_M \leq 10^{15}

Input

Input is given from Standard Input in the following format:

M
d_1 c_1
d_2 c_2
:
d_M c_M

Output

Print the maximum possible number of rounds in the preliminary stage.

Sample Input 1

2
2 2
9 1

Sample Output 1

3

In this case, N = 229 contestants will participate in the first round. One possible progression of the preliminary stage is as follows:

229 contestants participate in Round 1, 49 contestants participate in Round 2, 13 contestants participate in Round 3, and 4 contestants advance to the finals.

Here, three rounds take place in the preliminary stage, which is the maximum possible number.

Sample Input 2

3
1 1
0 8
7 1

Sample Output 2

9

In this case, 1000000007 will participate in the first round.

Solution in C++14 (GCC 5.4.1) (judge verdict: Runtime Error)

#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rfor(i, m, n) for (int i = (m); i >= (n); --i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define range_it(a, l, r) (a).begin() + (l), (a).begin() + (r)

using namespace std;
using ll = long long;		using ld = long double;
using VB = vector<bool>;	using VVB = vector<VB>;
using VI = vector<int>;		using VVI = vector<VI>;
using VL = vector<ll>;		using VVL = vector<VL>;
using VS = vector<string>;	using VD = vector<ld>;
using PII = pair<int, int>;	using VP = vector<PII>;
using PLL = pair<ll, ll>;	using VPL = vector<PLL>;
template<class T>using PQ = priority_queue<T>;
template<class T>using PQS = priority_queue<T, vector<T>, greater<T>>;
constexpr int inf = (int)1e9;
constexpr ll inf_ll = (ll)1e18, MOD = 1000000007;
constexpr ld PI = M_PI, EPS = 1e-12;

// --- input --- //
#ifdef _WIN32
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#define fwrite_unlocked fwrite
#define fflush_unlocked _fflush_nolock
#endif
inline int gc() { return getchar_unlocked(); }
template<class T>inline void InputF(T& v) { cin >> v; }
inline void InputF(char& v) { while (isspace(v = gc())); }
inline void InputF(bool& v) { char c; InputF(c); v = c != '0'; }
inline void InputF(string& v) {
	v.clear(); char c; for (InputF(c); !isspace(c); c = gc())v += c;
}
inline void InputF(int& v) {
	bool neg = false; v = 0; char c; InputF(c);
	if (c == '-') { neg = true; c = gc(); }
	for (; isdigit(c); c = gc())v = v * 10 + (c - '0');
	if (neg)v = -v;
}
inline void InputF(long long& v) {
	bool neg = false; v = 0; char c; InputF(c);
	if (c == '-') { neg = true; c = gc(); }
	for (; isdigit(c); c = gc())v = v * 10 + (c - '0');
	if (neg)v = -v;
}
inline void InputF(double& v) {
	double dp = 1; bool neg = false, adp = false; v = 0; char c; InputF(c);
	if (c == '-') { neg = true; c = gc(); }
	for (; isdigit(c) || c == '.'; c = gc()) {
		if (c == '.')adp = true;
		else if (adp)v += (c - '0') * (dp *= 0.1);
		else v = v * 10 + (c - '0');
	}
	if (neg)v = -v;
}
template<class T, class U>inline void InputF(pair<T, U>& v) {
	InputF(v.first); InputF(v.second);
}
template<class T>inline void InputF(vector<T>& v) {
	for (auto& e : v)InputF(e);
}
template<class T>inline T InputF() { T v; InputF(v); return v; }
inline string GetLine() {
	string v; char c; for (InputF(c); c != '\n' && c != '\0'; c = gc())v += c; return v;
}
struct InputV {
	int n, m;
	InputV(int N) :n(N), m(0) {}
	InputV(pair<int, int> N) :n(N.first), m(N.second) {}
	template<class T>operator vector<T>() {
		vector<T> v(n); InputF(v); return v;
	}
	template<class T>operator vector<vector<T>>() {
		vector<vector<T>> v(n, vector<T>(m)); InputF(v); return v;
	}
};
struct Input {
	template<class T>operator T() { return InputF<T>(); }
	int operator--(int) { int v; InputF(v); v--; return v; }
	InputV operator[](int n) { return InputV(n); }
	InputV operator[](pair<int, int> n) { return InputV(n); }
	void operator()() {}
	template<class H, class...T>void operator()(H&& h, T&& ...t) {
		InputF(h); operator()(forward<T>(t)...);
	}
	template<class T>Input& operator,(T&& v) {
		InputF(v); return *this;
	}
}in;
#define input(T) InputF<T>()
#define INT input(int)
#define LL input(ll)
#define STR input(string)
#define inputs(T, ...) T __VA_ARGS__; in(__VA_ARGS__)
#define ini(...) inputs(int, __VA_ARGS__)
#define inl(...) inputs(ll, __VA_ARGS__)
#define ins(...) inputs(string, __VA_ARGS__)

// --- output --- //
struct BoolStr {
	const char* t, * f; BoolStr(const char* _t, const char* _f) :t(_t), f(_f) {}
}Yes("Yes", "No"), yes("yes", "no"), YES("YES", "NO"), Int("1", "0");
struct DivStr {
	const char* d, * l; DivStr(const char* _d, const char* _l) :d(_d), l(_l) {}
}spc(" ", "\n"), no_spc("", "\n"), end_line("\n", "\n"), comma(",", "\n"), no_endl(" ", "");
class Output {
	BoolStr B{ Yes }; DivStr D{ spc };
	void p(int v) {
		if (v < 0)putchar_unlocked('-'), v = -v;
		char b[10]; int i = 0;
		while (v)b[i++] = '0' + v % 10, v /= 10;
		if (!i)b[i++] = '0';
		while (i--)putchar_unlocked(b[i]);
	}
	void p(ll v) {
		if (v < 0)putchar_unlocked('-'), v = -v;
		char b[20]; int i = 0;
		while (v)b[i++] = '0' + v % 10, v /= 10;
		if (!i)b[i++] = '0';
		while (i--)putchar_unlocked(b[i]);
	}
	void p(bool v) { p(v ? B.t : B.f); }
	void p(char v) { putchar_unlocked(v); }
	void p(const char* v) { fwrite_unlocked(v, 1, strlen(v), stdout); }
	void p(double v) { printf("%.20f", v); }
	void p(ld v) { printf("%.20Lf", v); }
	template<class T> void p(const T& v) { cout << v; }
	template<class T, class U>void p(const pair<T, U>& v) { p(v.first); p(D.d); p(v.second); }
	template<class T>void p(const vector<T>& v) { rep(i, sz(v)) { if (i)p(D.d); p(v[i]); } }
	template<class T>void p(const vector<vector<T>>& v) { rep(i, sz(v)) { if (i)p(D.l); p(v[i]); } }
public:
	Output& operator()() { p(D.l); return *this; }
	template<class H>Output& operator()(H&& h) { p(h); p(D.l); return *this; }
	template<class H, class...T>Output& operator()(H&& h, T&& ...t) {
		p(h); p(D.d); return operator()(forward<T>(t)...);
	}
	template<class...T>void exit(T&& ...t) { operator()(forward<T>(t)...); std::exit(EXIT_SUCCESS); }
	Output& flush() { fflush_unlocked(stdout); return *this; }
	Output& set(const BoolStr& b) { B = b; return *this; }
	Output& set(const DivStr& d) { D = d; return *this; }
	Output& set(const char* t, const char* f) { B = BoolStr(t, f); return *this; }
}out;

// --- step --- //
template<class T>struct Step {
	class It {
		T a, b, c;
	public:
		constexpr It() : a(T()), b(T()), c(T()) {}
		constexpr It(T _b, T _c, T _s) : a(_b), b(_c), c(_s) {}
		constexpr It& operator++() { --b; a += c; return *this; }
		constexpr It operator++(int) { It tmp = *this; --b; a += c; return tmp; }
		constexpr const T& operator*()const { return a; }
		constexpr const T* operator->()const { return &a; }
		constexpr bool operator==(const It& i)const { return b == i.b; }
		constexpr bool operator!=(const It& i)const { return !(b == i.b); }
		constexpr T start()const { return a; }
		constexpr T count()const { return b; }
		constexpr T step()const { return c; }
	};
	constexpr Step(T b, T c, T s) : be(b, c, s) {}
	constexpr It begin()const { return be; }
	constexpr It end()const { return en; }
	constexpr T start()const { return be.start(); }
	constexpr T count()const { return be.count(); }
	constexpr T step()const { return be.step(); }
	constexpr T sum()const { return start() * count() + step() * (count() * (count() - 1) / 2); }
	operator vector<T>()const { return as_vector(); }
	template<class F>void each(const F& f)const { for (T i : *this)f(i); }
	vector<T> as_vector()const {
		vector<T> res; res.reserve(count()); each([&](T i) {res.push_back(i); }); return res;
	}
	template<class F, class U = decay_t<result_of_t<F(T)>>>auto map(const F& f)const {
		vector<U> res; res.reserve(count()); each([&](T i) {res.push_back(f(i)); }); return res;
	}
	template<class F>vector<T> select(const F& f)const {
		vector<T> res; each([&](T i) {if (f(i))res.push_back(i); }); return res;
	}
	template<class F>int count_if(const F& f)const { int res = 0; each([&](T i) {if (f(i))++res; }); return res; }
	template<class F>T find_if(const F& f)const { for (T i : *this)if (f(i))return i; return 0; }
	template<class F>auto max_by(const F& f)const { auto v = map(f); return *max_element(v.begin(), v.end()); }
	template<class F>auto min_by(const F& f)const { auto v = map(f); return *min_element(v.begin(), v.end()); }
	template<class F, class U = decay_t<result_of_t<F(T)>>>auto sum(const F& f)const {
		U res = 0; each([&](T i) {res += static_cast<U>(f(i)); }); return res;
	}
	using value_type = T;
	using iterator = It;
private:
	It be, en;
};
template<class T>inline constexpr auto step(T a) { return Step<T>(0, a, 1); }
template<class T>inline constexpr auto step(T a, T b) { return Step<T>(a, b - a, 1); }
template<class T>inline constexpr auto step(T a, T b, T c) { return Step<T>(a, a < b ? (b - a - 1) / c + 1 : 0, c); }

// --- functions --- //
inline namespace {
	template<class T>inline void Sort(T& a) { sort(all(a)); }
	template<class T>inline void RSort(T& a) { sort(rall(a)); }
	template<class T>inline T Sorted(T a) { Sort(a); return a; }
	template<class T>inline T RSorted(T a) { RSort(a); return a; }
	template<class T, class F>inline void Sort(T& a, const F& f) {
		sort(all(a), [&](const auto& x, const auto& y) {return f(x) < f(y); });
	}
	template<class T, class F>inline void RSort(T& a, const F& f) {
		sort(rall(a), [&](const auto& x, const auto& y) {return f(x) < f(y); });
	}
	template<class T>inline void Reverse(T& a) { reverse(all(a)); }
	template<class T>inline void Unique(T& a) { a.erase(unique(all(a)), a.end()); }
	template<class T>inline void Rotate(T& a, int left) { rotate(a.begin(), a.begin() + left, a.end()); }
	template<class T>inline T Reversed(T a) { Reverse(a); return a; }
	template<class T>inline T Uniqued(T a) { Unique(a); return a; }
	template<class T>inline T Rotated(T a, int left) { Rotate(a, left); return a; }
	template<class T>inline auto Max(const T& a) { return *max_element(all(a)); }
	template<class T>inline auto Min(const T& a) { return *min_element(all(a)); }
	template<class T>inline int MaxPos(const T& a) { return max_element(all(a)) - a.begin(); }
	template<class T>inline int MinPos(const T& a) { return min_element(all(a)) - a.begin(); }
	template<class T, class F>inline auto Max(const T& a, const F& f) {
		return *max_element(all(a), [&](const auto& x, const auto& y) {return f(x) < f(y); });
	}
	template<class T, class F>inline auto Min(const T& a, const F& f) {
		return *min_element(all(a), [&](const auto& x, const auto& y) {return f(x) < f(y); });
	}
	template<class T, class U>inline int Count(const T& a, const U& v) { return count(all(a), v); }
	template<class T, class F>inline int CountIf(const T& a, const F& f) { return count_if(all(a), f); }
	template<class T, class U>inline int Find(const T& a, const U& v) { return find(all(a), v) - a.begin(); }
	template<class T, class F>inline int FindIf(const T& a, const F& f) { return find_if(all(a), f) - a.begin(); }
	template<class T, class U = typename T::value_type>inline U Sum(const T& a) { return accumulate(all(a), U()); }
	template<class T, class F>inline auto Sum(const T& v, const F& f) {
		return accumulate(next(v.begin()), v.end(), f(v.front()), [&](auto a, auto b) {return a + f(b); });
	}
	template<class T, class U>inline int Lower(const T& a, const U& v) { return lower_bound(all(a), v) - a.begin(); }
	template<class T, class U>inline int Upper(const T& a, const U& v) { return upper_bound(all(a), v) - a.begin(); }
	template<class T, class F>inline void RemoveIf(T& a, const F& f) { a.erase(remove_if(all(a), f), a.end()); }
	template<class F>inline auto Vector(size_t size, const F& f) {
		vector<decay_t<result_of_t<F(size_t)>>> res(size); for (size_t i = 0; i < size; ++i)res[i] = f(i); return res;
	}
	template<class T>inline auto Grid(size_t h, size_t w, const T& v = T()) { return vector<vector<T>>(h, vector<T>(w, v)); }
	template<class T>inline auto Slice(const T& v, size_t i, size_t len) {
		return i < v.size() ? T(v.begin() + i, v.begin() + min(i + len, v.size())) : T();
	}
	template<class T, class F>inline auto Each(const T& v, const F& f) { for (auto& i : v)f(i); }
	template<class T, class F>inline auto Select(const T& v, const F& f) {
		T res; for (const auto& e : v)if (f(e))res.push_back(e); return res;
	}
	template<class T, class F>inline auto Map(const T& v, const F& f) {
		vector<decay_t<result_of_t<F(typename T::value_type)>>> res(v.size());
		size_t i = 0; for (const auto& e : v)res[i++] = f(e); return res;
	}
	template<class T, class F>inline auto MapIndex(const T& v, const F& f) {
		vector<decay_t<result_of_t<F(size_t, typename T::value_type)>>> res(v.size());
		size_t i = 0; for (auto it = v.begin(); it != v.end(); ++it, ++i)res[i] = f(i, *it); return res;
	}
	template<class T, class F>inline auto TrueIndex(const T& v, const F& f) {
		vector<size_t> res; for (size_t i = 0; i < v.size(); ++i)if (f(v[i]))res.push_back(i); return res;
	}
	inline string operator*(string s, size_t n) { string ret; for (size_t i = 0; i < n; ++i)ret += s; return ret; }
	template<class T>inline T Ceil(T n, T m) { return (n + m - 1) / m; }
	template<class T>inline T Ceil2(T n, T m) { return Ceil(n, m) * m; }
	template<class T>inline T Tri(T n) { return (n & 1) ? (n + 1) / 2 * n : n / 2 * (n + 1); }
	template<class T>inline T nC2(T n) { return (n & 1) ? (n - 1) / 2 * n : n / 2 * (n - 1); }
	template<class T>inline T Mid(const T& l, const T& r) { return l + (r - l) / 2; }
	inline int pop_count(int n) { return bitset<32>(n).count(); }
	inline int pop_count(ll n) { return bitset<64>(n).count(); }
	template<class T>inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
	template<class T>inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
	template<class T>inline bool inRange(const T& v, const T& min, const T& max) { return min <= v && v < max; }
	template<class T = ll>inline T BIT(int b) { return T(1) << b; }
	template<class T>inline T Gcd(T n, T m) { return m ? Gcd(m, n % m) : n; }
	template<class T>inline T Lcm(T n, T m) { return n / Gcd(n, m) * m; }
	template<class T, class U = typename T::value_type>inline U Gcdv(const T& v) {
		return accumulate(next(v.begin()), v.end(), U(*v.begin()), Gcd<U>);
	}
	template<class T, class U = typename T::value_type>inline U Lcmv(const T& v) {
		return accumulate(next(v.begin()), v.end(), U(*v.begin()), Lcm<U>);
	}
	template<class T>inline T Pow(T a, T n) { T r = 1; while (n > 0) { if (n & 1)r *= a; a *= a; n /= 2; } return r; }
	template<class T>inline T Powmod(T a, T n, T m = MOD) {
		T r = 1; while (n > 0) { if (n & 1)r = r * a % m, n--; else a = a * a % m, n /= 2; }return r;
	}
}

// --- dump --- //
#if __has_include("dump.hpp")
#include "dump.hpp"
#else
#define dump(...) ((void)0)
#endif

// ---------------------------------------------------------------- //

int main() {
	ini(m);
	VI d(m); VL c(m);
	rep(i, m)in(d[i], c[i]);

	ll ans = 0;
	auto next = [&](int d1, int d2) {
		if (d1 + d2 < 10) {
			return make_pair(d1 + d2, 1);
		} else {
			int N = d1 + d2;
			return make_pair(N % 10 + N / 10, 2);
		}
	};
	function<int(int, int)> dfs = [&](int digit, ll cnt) {
		if (cnt == 1) {
			return digit;
		} else if (cnt % 2 == 0) {
			int N, C; tie(N, C) = next(digit, digit);
			ans += C * (cnt / 2);
			return dfs(N, cnt / 2);
		} else {
			int N, C; tie(N, C) = next(digit, digit);
			ans += C * (cnt / 2);
			int res = dfs(N, cnt / 2);
			int N2, C2; tie(N2, C2) = next(res, digit);
			ans += C2;
			return N2;
		}
	};

	VI D(m);
	rep(i, m) {
		D[i] = dfs(d[i], c[i]);
	}
	while (sz(D) > 1) {
		int e1 = D.back(); D.pop_back();
		int e2 = D.back(); D.pop_back();
		int N, C; tie(N, C) = next(e1, e2);
		ans += C;
		D.push_back(N);
	}
	out(ans);
}