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1044.cpp
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1044.cpp
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#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<queue>
#include<vector>
#define IL inline
#define re register
#define LL long long
#define ULL unsigned long long
#define re register
using namespace std;
template<class T>inline void read(T&x)
{
char ch=getchar();
while(!isdigit(ch))ch=getchar();
x=ch-'0';ch=getchar();
while(isdigit(ch)){x=x*10+ch-'0';ch=getchar();}
}
inline int read()
{
int x=0;
char ch=getchar();
while(!isdigit(ch))ch=getchar();
x=ch-'0';ch=getchar();
while(isdigit(ch)){x=x*10+ch-'0';ch=getchar();}
return x;
}
int G[55];
template<class T>inline void write(T x)
{
int g=0;
do{G[++g]=x%10;x/=10;}while(x);
for(int i=g;i>=1;--i)putchar('0'+G[i]);putchar('\n');
}
int n;
LL ans;
int a,b,c;
int memory[1000000];
bool had[1000000];
int calc()
{
return a*20+b;
}
int dfs()
{
if(had[calc()]) return memory[calc()];
int res=0;
if(c==n) return 1;
if(a){
b++;
a--;
res+=dfs();
a++;
b--;
}
if(b){
c++;
b--;
res+=dfs();
c--;
b++;
}
had[calc()]=1;
return memory[calc()]=res;
}
int main()
{
cin>>n;
a=n;
cout<<dfs();
return 0;
}