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

double x(int n) {
    double sum = 1.0; 
    int i;
    for (i = 1; i < n; i++) { 
        sum += pow(-1, i) / (2 * i + 1); 
    }
    return 4 * sum;
}

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