#include <iostream>
#include <math.h>
using namespace std;
int main() {
double sum = 0,fct = 1.,an = 1.,n = 1.;
const double e=0.00001;
while( an > e )
{
sum += an;
n++;
fct*= n;
an=fct /3 * pow(n,n);
}
cout<<sum;
return 0;
}
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