bzoj1002

#include<bits/stdc++.h>
using namespace std;
struct big
{
    int a[101],len;
};
int n;
big cf(big a,int k)
{
    for (int i=1;i<=a.len;i++)a.a[i]*=k;
    for (int i=1;i<=a.len;i++)
     {
        a.a[i+1]+=a.a[i]/10;
        a.a[i]%=10;
     }
    if (a.a[a.len+1]!=0)a.len++;
    return a;
} 
big jf(big a,big b)
{
    a.a[1]+=2;
    int j=1;
    while (a.a[j]>=10){a.a[j]%=10;a.a[j+1]++;j++;} 
    for (int i=1;i<=a.len;i++)
     {
        a.a[i]-=b.a[i];
        if(a.a[i]<0){a.a[i]+=10;a.a[i+1]--;}
     }
    while (a.a[a.len]==0)a.len--;
    return a;
}
int main()
{
    big f[101];f[1].a[1]=1;f[2].a[1]=5;
    f[1].len=f[2].len=1;
    scanf("%d",&n);
    for (int i=3;i<=n;i++)f[i]=jf(cf(f[i-1],3),f[i-2]);
    for (int i=f[n].len;i;i--)printf("%d",f[n].a[i]);
    return 0;
}