#include <stdio.h>



double f(double z, int k){
  if(k == 0) return z;
  else return (((-1)*z*z)/(2*k+1)*(2*k))*f(z,k-1);
}

int main(){
  float z = 0.5;
  int k;
  float rez;
  do {
    printf("Unesite k:\n");
    scanf("%d", &k);
    rez = f(z,k);
    printf("%f", rez);
  } while(1);
return 0;
}