#include<stdio.h>
#include<math.h>
int main()
{
long num,i,j,bin,paici,a,b,p,q,ans;
while(scanf("%ld",&num)==1)
{
if(num==0) break;
ans=0;
for(i=3;i!=0;i+=2)
{
bin=1;
paici=1;
a=i;
b=num-i;
if(a>b) break;
if(a%2!=0)
{
p=(int)sqrt(a);
for(j=3;j<=p;j+=2)
{
if(a%j==0)
{
bin=0; break;
}
}
if(bin==1)
{
if(b%2!=0)
{
q=(int)sqrt(b);
for(j=3;j<=q;j+=2)
{
if(b%j==0)
{
paici=0; break;
}
}
if(paici==1)
ans=ans+1;
}
}
}
}
if(num==4)
printf("1\n");
else
printf("%ld\n",ans);
}
return 0;
}
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