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#include<stdio.h>
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int su(int a)
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{
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int i,t=1;
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for(i=2;i<=a/2;i++)
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if(a%i==0)
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{
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t=0;break;
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}
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return t;
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}
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int main()
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{
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int n,i,a,b,j;
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while(~scanf("%d",&n))
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{
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if(n==0)return 0;
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int count=0;
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for(i=2;i<n/2;i++)
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{
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j=n-i;
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if(su(i)==1&&su(j)==1)
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{count++; }
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}
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printf("%d\n",count);
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}
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}
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