extern crate chrono;

use chrono::NaiveDate;
use chrono::Duration;

fn from_days_since_1900(days_since_1900: i64) -> NaiveDate {
    let d1900 = NaiveDate::from_ymd(1900, 1, 1);
    d1900 + Duration::days(days_since_1900)
}

fn main() {
    println!("{}", from_days_since_1900(40000));
}