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Cod sursa(job #401912)
#include<stdio.h>
#include<math.h>
#include<iostream.h>
FILE *f=fopen("12perm.in","r");
FILE *g=fopen("12perm.out","w");
long n,st[15000001],k,x;
int valid(int k){
int i;
for(i=1;i<k;i++){
if(st[i]==st[k])
return 0;
if(abs(st[i]-st[i+1])>=3)
return 0;}
return 1;}
void back(int k){
int i;
for(i=1;i<=n;i++){
st[k]=i;
if(valid(k))
if(k==n)
x++;
else
back(k+1);}}
int main (){
fscanf(f,"%ld",&n);
back(1);
fprintf(g,"%ld",x);
fclose(f);
fclose(g);
return 0;}