OJ-Problems-Source/HDOJ/2407_autoAC.cpp

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#include <iostream>
using namespace std ;
int main()
{
int n ;
while(~scanf("%d",&n))
{
double ans=1 ;
for(int i=n-1;i>=2;i-=2)
ans*=(i-1)*1.0/i ;
printf("%.5lf\n",ans) ;
}
return 0 ;
}