#include<bits/stdc++.h>
using namespace std;

#define int long long

typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define endl '\n'
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int N;
string ans;

int f(int x){
    int tmp=26,ret=0;
    rep(i,x){
        ret+=tmp;
        tmp*=26;
    }
    return ret;
}

signed main(){
    cin>>N;
    int c=0;
    while(f(c)<N+1)c++;

    N-=f(c-1);
    rep(i,c){
        ans+='A'+N%26;
        N/=26;
    }
    reverse(all(ans));
    cout<<ans<<endl;
}