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

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

int main() {
    int n1 = 3, n2 = 10;
    printf("x(%d) = %.6f\n", n1, calculate_series(n1));
    printf("x(%d) = %.6f\n", n2, calculate_series(n2));
    return 0;
}