#include <stdio.h>
int main(void) {
int n, last = 0, f = 1;
double res = 0;
for(int i=1; i <= n; i++) {
f *= i;
int sum = 0;
for(int k=last+1; k <= last + i; k++)
sum += k;
last += i;
res += 1.0 * f / (sum * sum);
}
return 0;
}
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