#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

int main() {
    char input[50];
    scanf("%s", input);

    // Check if input is numeric
    for (int i = 0; input[i] != '\0'; i++) {
        if (!isdigit(input[i])) {
            printf("Invalid input\n");
            return 0;
        }
    }

    long long n = atoll(input); // convert to number
    if (n <= 0) {
        printf("Invalid input\n");
        return 0;
    }

    char result[50];
    int index = 0;

    while (n > 0) {
        n--;  // adjust for 1-based index
        result[index++] = 'A' + (n % 26);
        n /= 26;
    }

    result[index] = '\0';

    // reverse string
    for (int i = 0; i < index / 2; i++) {
        char temp = result[i];
        result[i] = result[index - 1 - i];
        result[index - 1 - i] = temp;
    }

    printf("%s\n", result);
    return 0;