#include <cstdio>
#include <cstring>
#include <cassert>
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <vector>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
using namespace std;
const int N = 114514;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
void fast()
{
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
int dp[N][20], cnt[N][20];
int main()
{
fast();
int n;
while (cin >> n && n != 0)
{
memset(cnt, 0, sizeof (cnt));
memset(dp, 0, sizeof (dp));
int timemax = -1;
for (int i = 1; i <= n; ++i)
{
int x, t;
cin >> x >> t;
cnt[t][x]++;
timemax = max(timemax, t);
}
for (int i = timemax; i >= 0; --i)
{
for (int j = 0; j <= 10; ++j)
{
int temp = -1;
if (j - 1 >= 0)
{
temp = max(temp, dp[i + 1][j - 1]);
}
temp = max(temp, dp[i + 1][j]);
if (j + 1 <= 10)
{
temp = max(temp, dp[i + 1][j + 1]);
}
dp[i][j] = cnt[i][j] + temp;
}
}
cout << dp[0][5];
}
}