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