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

long double my_abs (long double data);

void ans (long double x);

long double input_check ();

void input (long double& x);


int main() {

    long double x;
    input(x);

    ans(x);
    printf("Math.h says: %Lf\n", cosh(x));
    return 0;

}


long double my_abs (long double data) {

    if (data < 0) {
        return (-1)*(data);
    } else {
        return data;
    }

}

void ans (long double x) {

    long double next, prev, eps, sum;
    prev = 1.0;
    next = (prev*x*x)/(2*1);
    sum = 1.0;

    int k = 2;
    while (true) {

        prev = next;
        sum += next;
        next = (prev*x*x)/((2*k)*(2*k - 1));

        eps = my_abs(next - prev);
        if (eps <= 0.00001) {
            printf("K: %d\nVash chosinus: %Lf\n", k, sum);
            break;
        }

        ++k;

    }

}

long double input_check() {

    long double data;
    int len = 0;
    char ch;
    char* str = (char*)malloc(sizeof(char));
    printf("Vvedi x:\n");
    while (1) {

        ch = getchar();
        if (ch == '\n') {
            break;
        } else {
            str[len] = ch;
            str = (char*)realloc(str,(1 + (++len)*sizeof(char)));
        }

    }

    data = atof(str);
    if (!len) {
        return -2;
    }
    if (data == 0 && str[0] != '0') {
        return -1;
    } else {
        return data;
    }

}

void input (long double& x) {

    while (1) {
        x = input_check();
        if (x == -1 || x == -2) {
            printf("Vvedite eshe raz\n");
            continue;
        } else {
            //printf("Data: %Lf\n", x);
            break;
        }
    }

}