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Cod sursa(job #544701)
#include<iostream.h>
#include<fstream.h>
long long x[100000],n,z=0;
ifstream f("12perm.in");
ofstream h("12perm.out");
int valid(int k)
{int i;
for(i=1;i<k;i++)
if(x[k]==x[i])
return 0;
if(x[k-1]-x[k]>=3||x[k-1]-x[k]<=-3)
return 0;
return 1;}
void back(int k)
{int i;
for(i=1;i<=n;i++)
{x[k]=i;
if(valid(k)==1)
if(k==n)
z++;
else
back(k+1);}}
int main()
{f>>n;
back(1);
h<<2*z;
return 0;}