#include <stdio.h>
#include <math.h>

double calculate_x(int n) {
    double sum = 0.0;
    for (int i = 0; i < n; i++) {
        double term = pow(-1, i) / (2 * i + 1);
        sum += term;
    }
    return 4 * sum;
}

int main() {
    int n1 = 3;
    int n2 = 10;
    
    double x_n1 = calculate_x(n1);
    double x_n2 = calculate_x(n2);
    
    printf("x(%d) = %f\n", n1, x_n1);
    printf("x(%d) = %f\n", n2, x_n2);
    
    return 0;
}