http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3625
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <stdio.h> 2 #include <math.h> 3 #define E 0.57721566490153286060651209 4 int main() 5 { 6 double a,x; 7 while (scanf("%lf",&a) != EOF) 8 { 9 10 x = E; 11 x *= pow(2,a) - 1; 12 printf("%1.12e\n",x); 13 } 14 return 0 ; 15 }