hdu 2013

#include <stdio.h>      int main(){    int x1,x2,n,i;    while (scanf("%d",&n)!=EOF)    {          x2=1;          if (n>1&&n<30)          {             for (i=1;i<n;i++)                  {                    x1=(x2+1)*2;                    x2=x1;                   }    printf ("%d/n",x1);                    }      } return 0;}