import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
{
Scanner in
=new Scanner
(System.
in); double a=in.nextDouble();
double b=in.nextDouble();
int n=in.nextInt();
if((n
<=0)||(a
==b
))System.
out.
println("Введенное 'n' не натуральное или введены два одинаковых числа\n"); else
if (a
>b
)System.
out.
println("Первое введеное число больше второго"); else
{
double h=(b-a)/n;
double f=0;
for(int i=1;i<=n;i++)
{
f+=(a+(i-0.5)*h)/(1+((a+(i-0.5)*h)*(a+(i-0.5)*h)));
}
}
}
}
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