/* yukicoder My Practice
 * autoher: Leonarone  NEETSDKASU
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

typedef long long ll;
typedef unsigned long long ull;

void solve(void);
int main(void) { solve(); return 0; }


void solve(void) {
    char ans[21] = {0}, *p = &ans[20];
    ll n, s = -1LL, d1 = 1LL, d2 = 26LL;
    scanf("%lld", &n);
    for (;;) {
        s += d1;
        if (s > n) break;
        *(--p) = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[(int)(((n - s) % d2) / d1)];
        d1 = d2;
        d2 *= 26LL;
    }
    puts(p);
}