17 lines
264 B
C++
17 lines
264 B
C++
#include<cstdio>
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#include<cmath>
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using namespace std;
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int main()
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{
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double three=sqrt(3),add=0,x;
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for(int i=1;i>0;i++)
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{
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x=(1.0/pow(three,i*2-1))/(double)(i*2-1);
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if(x<0.000001) break;
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if(i&1) add+=x;
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else add-=x;
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}
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printf("%g\n",6*add);
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return 0;
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}
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