Print number

#include <stdio.h>
#include <assert.h>
typedef long long ll;

void read_digit(ll n) {
    assert(n >= 0 && n <= 9);
    if (n == 1) printf("one");
    else if (n == 2) printf("two");
    else if (n == 3) printf("three");
    else if (n == 4) printf("four");
    else if (n == 5) printf("five");
    else if (n == 6) printf("six");
    else if (n == 7) printf("seven");
    else if (n == 8) printf("eight");
    else if (n == 9) printf("nine");
}

void read_two_digits(ll n) {
    assert(n >= 1 && n <= 99);
    if (n == 10) printf("ten");
    else if (n == 11) printf("eleven");
    else if (n == 12) printf("twelve");
    else if (n == 13) printf("thirteen");
    else if (n == 14) printf("fourteen");
    else if (n == 15) printf("fifteen");
    else if (n == 16) printf("sixteen");
    else if (n == 17) printf("seventeen");
    else if (n == 18) printf("eighteen");
    else if (n == 19) printf("nineteen");
    else {
        if (n/10 == 2) printf("twenty");
        else if (n/10 == 3) printf("thirty");
        else if (n/10 == 4) printf("forty");
        else if (n/10 == 5) printf("fifty");
        else if (n/10 == 6) printf("sixty");
        else if (n/10 == 7) printf("seventy");
        else if (n/10 == 8) printf("eighty");
        else if (n/10 == 9) printf("ninety");
        if (n/10 >= 2 && n%10 > 0) printf("-");
        read_digit(n%10);
    }
}

void read_three_digits(ll n) {
    assert(n >= 1 && n <= 999);
    if (n/100 > 0) {
        read_digit(n/100);
        printf(" hundred");
        if (n%100 > 0)
            printf(" and ");
    }
    read_two_digits(n%100);
}

// zone1 billion zone2 million zone3 thousand zone4
void read_num(ll n) {
    assert(n >= 0 && n <= (ll)1e12-1);
    if (n == 0) {
        printf("zero");
        return;
    }
    ll zone4 = n % 1000;
    ll zone3 = (n/1000) % 1000;
    ll zone2 = (n/1000000) % 1000;
    ll zone1 = (n/1000000000) % 1000;
    bool comma = false;
    if (zone1 > 0) {
        read_three_digits(zone1); printf(" billion"); comma = true;
    }
    if (zone2 > 0) {
        if (comma) printf(", ");
        read_three_digits(zone2); printf(" million"); comma = true;
    }
    if (zone3 > 0) {
        if (comma) printf(", ");
        read_three_digits(zone3); printf(" thousand"); comma = true;
    }
    if (zone4 > 0) {
        if (comma) printf(", ");
        read_three_digits(zone4); comma = true;
    }
}

int main(void) {
    ll n;
    scanf("%lld", &n);
    read_num(n);
    printf("\n");
}