const Main = input => {
    input = input.trim();
    const n = parseInt(input, 10) - 1;

    const convertedN = toNBase(n, 26).map(value => value + 0x60);
    convertedN[convertedN.length - 1] += 0x1;
    const result = String.fromCharCode(...convertedN);
    console.log(result);
}

//numをn進数に変換する
const toNBase = (num, n) => {
    const result = [];
    let q = num;
    while(true) {
        result.unshift(q % n);//余りを入れる
        q = Math.floor(q / n);

        if(q < n) {
            if(q !== 0) result.unshift(q);
            break;
        }
    }

    return result;
}
 
Main(require("fs").readFileSync("/dev/stdin", "utf8"));