//#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#include <map>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <ctime>
#include <algorithm>
#include <sstream>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <cstdlib>
#include <cstdio>
#include <iterator>
#include <functional>
#include <bitset>
#define mp make_pair
#define pb push_back

#ifdef LOCAL
#define eprintf(...) fprintf(stderr,__VA_ARGS__)
#else
#define eprintf(...)
#endif

#define TIMESTAMP(x) eprintf("["#x"] Time : %.3lf s.\n", clock()*1.0/CLOCKS_PER_SEC)
#define TIMESTAMPf(x,...) eprintf("[" x "] Time : %.3lf s.\n", __VA_ARGS__, clock()*1.0/CLOCKS_PER_SEC)

#if ( ( _WIN32 || __WIN32__ ) && __cplusplus < 201103L)
    #define LLD "%I64d"
#else
    #define LLD "%lld"
#endif

using namespace std;

#define TASKNAME "pwgen"

#ifdef LOCAL
static struct __timestamper {
    string what;
    __timestamper(const char* what) : what(what){};
    __timestamper(const string& what) : what(what){};
	~__timestamper(){
        TIMESTAMPf("%s", what.data());
	}
} __TIMESTAMPER("end");
#else 
struct __timestamper {};
#endif

typedef long long ll;
typedef long double ld;


int main(){
    assert(freopen(TASKNAME".in","r",stdin));
    assert(freopen(TASKNAME".out","w",stdout));

  	int n, a, b, c;
  	scanf("%d%d%d%d",&n,&a,&b,&c);

  	for (int i = 0; i < a; i++)
  		printf("%c", 'A' + i % 26);
  	for (int i = a; i < a+b; i++)
  		printf("%c", 'a' + i % 26);
  	for (int i = a+b; i < a+b+c; i++)
  		printf("%c", '0' + i % 10);
  	for (int i = a+b+c; i < n; i++)
  		printf("%c", 'a' + i % 26);
    return 0;
}