#include<bits/stdc++.h>
using namespace std;
#define fi first
#define sc second
#define pii pair<int,int>
#define pdd pair<double,double>
#define pb push_back
#define umap unordered_map
#define mset multiset
#define pq priority_queue
#define ull unsigned long long
#define i128 __int128
#define ld long double
#define fixs fixed<<setprecision
const int maxn=2000+10;
int n,a[maxn],b[maxn],f[maxn][maxn];
void chkmax(int &x,int y){
    x=max(x,y);
}
void solve(){
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i]>>b[i];
    for(int i=1;i<=n;i++){
        int minn=1e9;
        for(int j=0;j<=2000;j++) f[i][j]=f[i-1][j];
        for(int j=1;j<=b[i];j++) chkmax(f[i][max(j,a[i])],f[i-1][j-1]+1);
    }
    cout<<*max_element(f[n]+1,f[n]+2001)<<endl;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    int t=1;
    // cin>>t;
    while(t--) solve();
    return 0;
}
/*
Samples
input:

output:

THINGS TODO:
检查freopen，尤其是后缀名
检查空间
检查调试语句是否全部注释
*/