#include <stdio.h>

int main() {
  double xp[3] = {0, 1, 2};
  double yp[3] = {1, 4, 9};
  double x = 1.5;
  double y = 0;
  for (int i = 0; i < 3; i++) {
    double L = 1;
    for (int j = 0; j < 3; j++) {
      if (j != i) L *= (x - xp[j]) / (xp[i] - xp[j]);
    }
    y += yp[i] * L;
  }
  printf("P(%.1f) = %.4f\n", x, y);
  return 0;
}