POJ 2591

 1 #include<iostream>
 2 #include<stdio.h>
 3 #define MAXN  10000001
 4 using namespace std;
 5 
 6 int a[MAXN];
 7 void give_set();
 8 int min(int i,int j);
 9 int main()
10 {
11     //freopen("acm.acm","r",stdin);
12     give_set();
13     int num;
14     while(cin>>num)
15     {
16         cout<<a[num-1]<<endl;
17     }
18 }
19 
20 void give_set()
21 {
22     a[0] = 1;
23     int m;
24     int len = 1;
25     int x;
26     int y;
27     x = 0;
28     y = 0;
29     while(len < MAXN)
30     {
31         m = min(2*a[x]+1,3*a[y]+1);
32         if(m == 2*a[x]+1) 
33             ++ x;
34         if(m == 3*a[y]+1)
35             ++ y;
36         a[len++] = m;
37     }
38 }
39 int min(int a,int b)
40 {
41     return a < b ? a : b;
42 }