#include <bits/stdc++.h>
#define l first
#define r second
using namespace std;
int solve3()
{
int K;
vector<pair<int, int>> Q;
cin >> K;
vector<int> dp(K, 1);
for (int i = 0; i < K; i++)
{
int L, R;
cin >> L >> R;
Q.push_back({L, R});
}
for (int i = 1; i < K; i++)
{
if (i > Q[i].l)
{
for (int j = 0; j < i - Q[i].l; j++)
{
if (j + Q[j].r < i)
{
// cout << i << " " << j << "\n";
dp[i] = max(dp[i], dp[j] + 1);
}
}
}
}
// for (int x : dp)
// {
// cout << x << " ";
// }
// cout << "\n";
return *max_element(dp.begin(), dp.end());
}
int solve4()
{
int K;
vector<pair<int, int>> Q;
cin >> K;
vector<int> dp(K, 1);
for (int i = 0; i < K; i++)
{
int L, R;
cin >> L >> R;
Q.push_back({L, R});
}
for (int i = 1; i < K; i++)
{
if (i > 2)
dp[i] = dp[i - 3] + 1;
for (int j = 2; j > Q[i].l; j--)
{
if (i - j >= 0 && j + Q[i - j].r < i)
{
dp[i] = max(dp[i - j] + 1, dp[i]);
}
}
}
return *max_element(dp.begin(), dp.end());
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout << solve4();
}
