#include <iostream>
#include <iomanip>
#include <vector>
#include <set>
#include <string>
#include <queue>
#include <algorithm>
#include <map>
#include <cmath>
#include <numeric>
#include <list>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <tuple>

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define show(a, n) rep(i,n) {cout<<a[i]<<' ';} cout<<endl
#define show2(a, n, m) rep(i, n) { rep(j, m) {cout << a[i][j] << ' ';} cout << endl;} 
#define chmin(a, b) a = min(a, b)
#define chmax(a, b) a = max(a, b)

using namespace std;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef long long ll;
typedef vector<ll> vll;
typedef pair<long long, long long> pll;
typedef long double ld;

const int INF = 1 << 30;
const long long INFL = 1LL << 60;
const int MOD = 1000000007;
const int MAX = 100000;
const int N = 100010;

int main() {
//	cout << fixed << setprecision(15);
	ll m;
	cin >> m;
	vll d(m), c(m);
	rep(i, m) cin >> d[i] >> c[i];

	ll sumc = 0;
	ll sumd = 0;
	rep(i, m) sumc += c[i];
	rep(i, m) sumd += c[i] * d[i];

	cout << sumc - 1 + (sumd - 1) / 9 << endl;
}

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int solve(int n, vector<int> & dims){
    int dp[100][101] = {{0}};
    for (int span = 2; span != n + 1; ++span){
        for (int first = 0; first + span != n + 1; ++first){
            for (int last = first + span; last != n + 1; ++last){
                int record = 2000000000;
                for (int mid = first + 1; mid != last; ++mid){
                    record = min(record, dp[first][mid] + dp[mid][last] + dims[first] * dims[last] * dims[mid]);
                }
                dp[first][last] = record;
            }
        }
    }
    return dp[0][n];
}


int main()
{
    int n = 0;
    cin >> n;
    vector<int> dims(n + 1);
    int r = 0;
    int c = 0;
    for (int i = 0; i != n; ++i){
        cin >> r >> c;
        dims[i] = r;
    }
    dims[n] = c;
    cout << solve(n, dims) << endl;
    return 0;
}