为什么求最长上升子序列时，把lower_bound换成upper_bound就出错了啊

#include <iostream>
#include <algorithm>
using namespace std;

int num[100020];
int st1[100020], st2[100020];
int cnt = 0;
int top1 = 1;
int top2 = 1;
int main(){
	while(cin>>num[++cnt]);
	cnt -= 1;
	st1[1] = num[1];
	st2[1] = num[1];
	for(int i = 2; i <= cnt; i++){
		if(num[i] <= st1[top1]){
			st1[++top1] = num[i];
		}
		else{
			int k = upper_bound(st1 + 1, st1 + 1 + top1, num[i], greater<int>() ) - st1;
			st1[k] = num[i];  
		}
		
		if(num[i] > st2[top2]){
			st2[++top2] = num[i];
		}
		else{
			int k = upper_bound(st2 + 1, st2 + 1 + top2, num[i]) - st2;
			st2[k] = num[i];
		}
	}
	cout<<top1<<endl<<top2;
	return 0;
}