usaco09dec selfish grazing

#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef pair<int,int> P;
P p[50005];
int (){
    int n,i,j,u,v,ans=0;
    scanf("%d",&n);
    for(i=0;i<n;i++)
        scanf("%d%d",&u,&v),
        p[i].first=v,p[i].second=u;
    sort(p,p+n);
    ans++,u=p[0].second,v=p[0].first;
    for(i=1;i<n;){
        while(i<n&&p[i].second<v)
            i++;
        if(i==n)break;
        ans++,u=p[i].second,v=p[i].first;
    }
    printf("%dn",ans);
    return 0;
}