能帮我看看为什么lower_bound为什么报错 int is not a class吗 感谢！！！

using namespace std;
#include<bits/stdc++.h>
#define ll long long
const int N=1e5+7;
ll read(){
   ll summ=0;ll f=1;char ch;
   ch=getchar();
   while(ch<'0'||ch>'9'){
	   if(ch=='-'){
		   f=-1;
	   }
	   ch=getchar();
   
   }
   while(ch>='0'&&ch<='9'){
	   summ=summ*10+ch-'0';
	   ch=getchar();
   
   }
   return f*summ;

}
int n=1;
int ar[N];
int f1[N];
int f2[N];    
int main(){
	while(cin>>ar[n]){
        n++; 
    }
    n--;
//	cout<<ar[1]; 
//	for(int i=1;i<=n;i++){
//		f1[i]=1;
//	} 
	int len1=1;
	
	f1[1]=ar[1];
	for(int i=2;i<=n;i++){
		if(f1[len1]>=ar[i]){
			len1++;
			f1[len1]=ar[i];
		}else{
			f1[lower_bound(1,n,ar[i],greater< int >())]=ar[i];
		}
		
	}
	cout<<len1;
}