丑数，4遍提交耻辱啊。

Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, …
shows the first 11 ugly numbers. By convention, 1 is included.
Write a program to find and print the 1500’th ugly number.
Input
There is no input to this program.
Output
Output should consist of a single line as shown below, with ‘< number >’ replaced by the number
computed.
Sample Output
The 1500’th ugly number is < number >.

#include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<set>
#include<algorithm>
using namespace std;
int main()
{
    set<int> a;
    set<int> b;
    set<int>::iterator p1,p2;
    a.insert(1);
    a.insert(2);
    a.insert(3);
    a.insert(4);
    a.insert(5);
    a.insert(6);
    a.insert(8);
    a.insert(9);
    for(p1=a.begin();p1!=a.end();p1++)
    {
        a.insert(*p1*2);
        a.insert(*p1*3);
        a.insert(*p1*5);
        if(a.size()>1600) break;
    }
    p1=a.begin();
    for(int i=1;i<1500;i++)
    {
        p1++;
    }
    	printf("The 1500'th ugly number is %d.\n",*p1);
}

算出来的数，跟网上查的是一样的，四遍就是过不去，后来发现，自己“ 点 ”的位置不对。换行符没加。活该不对。