#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <functional>
#include <ctime>
#include <cmath>
#include <limits>
#include <numeric>
#include <type_traits>
#include <iomanip>
#include <float.h>
#include <math.h>
using namespace std;
using ll = long long;
unsigned euclidean_gcd(unsigned a, unsigned b) {
    if (a < b) return euclidean_gcd(b, a);
    unsigned r;
    while ((r = a % b)) {
        a = b;
        b = r;
    }
    return b;
}

ll ll_gcd(ll a, ll b) {
    if (a < b) return ll_gcd(b, a);
    ll r;
while ((r = a % b)) {
    a = b;
    b = r;
}
return b;
}

class UnionFind {
public:
    vector <ll> par;
    vector <ll> siz;
    UnionFind(ll sz_) : par(sz_), siz(sz_, 1LL) {
        for (ll i = 0; i < sz_; ++i) par[i] = i;
    }
    void init(ll sz_) {
        par.resize(sz_);
        siz.assign(sz_, 1LL);
        for (ll i = 0; i < sz_; ++i) par[i] = i;
    }
    ll root(ll x) {
        while (par[x] != x) {
            x = par[x] = par[par[x]];
        }
        return x;
    }
    bool merge(ll x, ll y) {
        x = root(x);
        y = root(y);
        if (x == y) return false;
        if (siz[x] < siz[y]) swap(x, y);
        siz[x] += siz[y];
        par[y] = x;
        return true;
    }

    bool issame(ll x, ll y) {
        return root(x) == root(y);
    }

    ll size(ll x) {
        return siz[root(x)];
    }
};

long long modpow(long long a, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}

long long modinv(long long a, long long mod) {
    return modpow(a, mod - 2, mod);
}

vector<int> tpsort(vector<vector<int>>& G) {
    int V = G.size();
    vector<int> sorted_vertices;
    queue<int> que;
    vector<int> indegree(V);
    for (int i = 0; i < V; i++) {
        for (int j = 0; j < G[i].size(); j++) {
            indegree[G[i][j]]++;
        }
    }
    for (int i = 0; i < V; i++) {
        if (indegree[i] == 0) {
            que.push(i);
        }
    }
    while (que.empty() == false) {
        int v = que.front();
        que.pop();
        for (int i = 0; i < G[v].size(); i++) {
            int u = G[v][i];
            indegree[u] -= 1;
            if (indegree[u] == 0) que.push(u);
        }
        sorted_vertices.push_back(v);
    }
    return sorted_vertices;
}

struct Point
{
    double x;
    double y;
};

struct LineSegment
{
    Point start;
    Point end;
};

double tenkyori(const LineSegment& line, const Point& point)
{
    double x0 = point.x, y0 = point.y;
    double x1 = line.start.x, y1 = line.start.y;
    double x2 = line.end.x, y2 = line.end.y;

    double a = x2 - x1;
    double b = y2 - y1;
    double a2 = a * a;
    double b2 = b * b;
    double r2 = a2 + b2;
    double tt = -(a * (x1 - x0) + b * (y1 - y0));

    if (tt < 0)
        return sqrt((x1 - x0) * (x1 - x0) + (y1 - y0) * (y1 - y0));
    else if (tt > r2)
        return sqrt((x2 - x0) * (x2 - x0) + (y2 - y0) * (y2 - y0));

    double f1 = a * (y1 - y0) - b * (x1 - x0);
    return sqrt((f1 * f1) / r2);
}

int main() {
    ll m;
    cin >> m;
    ll dig = 0;
    ll sum = 0;
    for (int i = 0; i < m; i++) {
        ll a, b;
        cin >> a >> b;
        dig += b;
        sum += a * b;
    }
    cout << dig - 1 + (sum-1) / 9 << endl;
}

Measured memory_bytes: 3688