#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
double ans=1,sum=1; //int型范围不够大,故用double
for(int i=2;i<=30;i++)
{
ans*=i;
sum+=ans;
}
cout<<setprecision(3)<<sum<<endl; //也可写成"cout<<setiosflags(ios::scientific)<<setprecision(2)<<endl;"
return 0;
}
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