ROT13
At first glance no idea 
then tried it ROT13, encryption again
`#include"stdio.h"
main()
{
int i;
char a[80];
sanf("%s",a);
for(i=0;a[i]!=0;i++)
{
if(a[i]>=‘a’&&a[i]<=‘m’)
a[i]=a[i]+13;
else if(a[i]>‘m’&&a[i]<=‘z’)
a[i]=a[i]-13;
}
a[i]=0;
puts(a);
}`
所以key就找到了。
key就是23ksdjfkfds.
