function main(input){
  const N = BigInt(input);

  let keta = 1;
  let st = 0n;
  let ed = 26n;
  while(true){
    if(N <= (ed+st)) break;
    keta++;
    st += ed;
    ed*=26n;
  }

  const arr = 'abcdefghijklmnopqrstuvwxyz';
  let n = N-(st+1n);
  let ret = '';
  for(let i=0; i<keta; i++){
    ret += arr[n%26n];
    n /= 26n;
  }
  console.log(ret.split('').reverse().join(''));
}

main(require('fs').readFileSync('/dev/stdin', 'utf8').trim());