//
// File "input.txt" contains a polynomial:
// first the number of its coefficients, then
// the coefficients in descending order.
// For example, for the polynomial
//     3*x^3 + 5^x^2 - 7^x + 1
// the file "input.txt" contains:
//     4
//     3 5 -7 1
//
// The program must write the coefficients of
// the derivative of this polynomial in descending order
// into the file "output.txt".
// In this example, the derivative of the polynomial is
//     9*x^2 + 10*x - 7,
// so the file "output.txt" should contain
//     9 10 -7
//
// The program should use the same array for the
// coefficients of polynomial (input data) and
// the resulting coefficient of derivative (output data).
//
#include <stdio.h>
#include <math.h>       /* Not necessary in this example */

void computeDerivative(double *a, int n);

int main() {
    // Open the input file
    FILE* f = fopen("input.txt", "rt");
    if (f == NULL) {
        perror("Cannot open the input file");
        return -1;
    }

    // Read the size of array
    int n;
    if ((fscanf(f, "%d", &n) < 1) || n <= 0) {
        printf("Illegal input file.\n");
        fclose(f);
        return -1;
    }

    // Allocate an array in dynamic memory
    double *a = new double[n];

    // Read coefficients of a polynomial
    for (int i = 0; i < n; ++i) {
        if (fscanf(f, "%lg", a + i) < 1) {
            printf("Incorrect format of input file.\n");
            fclose(f);
            delete[] a;
            return -1;
        }
    }
    fclose(f);

    computeDerivative(a, n);

    // Open the output file
    FILE* h = fopen("output.txt", "wt");
    if (h == NULL) {
        perror("Cannot open the output file");
        return -1;
    }

    if (n <= 1) {
        // Zero derivative
        fprintf(h, "0\n");
    } else {
        for (int i = 0; i < n-1; ++i) {
            if (i > 0) {
                fprintf(h, " "); // Write a separator
            }
            fprintf(h, "%g", a[i]);
        }
        fprintf(h, "\n"); // Write end of line
    }
    fclose(h);

    delete[] a;
    return 0;   // Success!
}

void computeDerivative(double *a, int n) {
    int deg = n - 1;    // Degree of a term
    int i = 0;          // Index of the term coefficient in array
    while (deg > 0) {
        a[i] *= deg;
        --deg;
        ++i;
    }
}