#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <string>#define CL(a,num) memset((a),(num),sizeof(a))
#define iabs(x)  ((x) > 0 ? (x) : -(x))
#define Min(a,b) (a) > (b)? (b):(a)
#define Max(a,b) (a) > (b)? (a):(b)#define ll __int64
#define inf 0x7f7f7f7f
#define MOD 100000007
#define lc l,m,rt<<1
#define rc m + 1,r,rt<<1|1
#define pi acos(-1.0)
#define test puts("<------------------->")
#define maxn 10000007
#define M 100007
#define N 507
using namespace std;
//freopen("din.txt","r",stdin);struct node{int l,r;int len;int num;
}seg[N];
int dp[N];
int n,length;int cmp(node a,node b){return a.l < b.l;
}
void insert(int l,int r){int i;for (i = 0; i < length; ++i){if (seg[i].l == l && seg[i].r == r){//如果已经存在并且还没有达到区间值就可添加if (seg[i].num < seg[i].len) seg[i].num++;break;}}if (i >= length){seg[length].l = l;seg[length].r = r;seg[length].len = r - l + 1;seg[length].num = 1;length++;}
}
bool isok(int i,int j){//printf("****%d %d %d %d\n",i,j,seg[i].r,seg[j].l);if (seg[i].l <= seg[j].r) return false;//判断区间是否相交else return true;
}
void solve(){int i,j;CL(dp,0);dp[0] = seg[0].num;//dp求值for (i = 1; i < length; ++i){for (j = 0; j < i; ++j){if (isok(i,j)){//puts("DDD");dp[i] = max(dp[i],dp[j] + seg[i].num);}}if (dp[i] == 0){dp[i] = seg[i].num;}}
}
int main(){//freopen("din.txt","r",stdin);int i;int Ai,Bi;while (~scanf("%d",&n)){length = 0;for (i = 0; i < n; ++i){scanf("%d%d",&Ai,&Bi);int R = n - Ai;int L = Bi + 1;if (L > R) continue;//这样的肯定不满足insert(L,R);//查看区间
        }sort(seg,seg + length,cmp);//for (i = 0; i < length; ++i) printf(">>>%d %d %d %d\n",seg[i].l,seg[i].r,seg[i].len,seg[i].num);
        solve();int MAX = -inf;for (i = 0; i < length; ++i){// printf(">>%d\n",dp[i]);MAX = max(MAX,dp[i]);}printf("%d\n",MAX);}return 0;
}