#include <bits/stdc++.h>
#pragma GCC diagnostic ignored "-Wincompatible-pointer-types"
typedef struct {
  int64_t a;
  int64_t b;
} hwll;
typedef struct {
  int64_t a;
  int64_t b;
  int64_t c;
} hwllc;
typedef struct {
  hwll a;
  hwll b;
} linell;
typedef struct {
  double a;
  double b;
} hwreal;
int64_t n, m;
int64_t h, w;
int64_t k;
int64_t q;
int64_t va, vb, vc, vd, ve, vf;
uint64_t ua, ub, uc, ud, ue, uf;
long double vra, vrb, vrc;
double vda, vdb, vdc;
char ch, dh;
uint64_t umin(uint64_t x, uint64_t y) { return (x < y) ? x : y; }
uint64_t umax(uint64_t x, uint64_t y) { return (x > y) ? x : y; }
int64_t smin(int64_t x, int64_t y) { return (x < y) ? x : y; }
int64_t smax(int64_t x, int64_t y) { return (x > y) ? x : y; }
uint64_t gcd(uint64_t x, uint64_t y) {
  if (y == 0) {
    return x;
  } else {
    return gcd(y, x % y);
  }
}
uint64_t bitpow(uint64_t a, uint64_t x, uint64_t modulo) {
  uint64_t result = 1;
  while (x) {
    if (x & 1) {
      result *= a;
      result %= modulo;
    }
    x /= 2;
    a = (a * a) % modulo;
  }
  return result;
}
uint64_t divide(uint64_t a, uint64_t b, uint64_t modulo) {
  return (a * bitpow(b, modulo - 2, modulo)) % modulo;
}
uint64_t udiff(uint64_t a, uint64_t b) {
  if (a >= b) {
    return a - b;
  } else {
    return b - a;
  }
}
int64_t sdiff(int64_t a, int64_t b) {
  if (a >= b) {
    return a - b;
  } else {
    return b - a;
  }
}
int bitcount(uint64_t n) {
  int result = 0;
  while (n) {
    if (n & 1) result++;
    n /= 2;
  }
  return result;
}
int32_t pullcomp(const void *left, const void *right) {
  uint64_t l = *(uint64_t *)left, r = *(uint64_t *)right;
  if ((l) < (r)) return -1;
  if ((l) > (r)) return +1;
  return 0;
}
int32_t prevcomp(const void *left, const void *right) {
  int64_t l = *(int64_t *)left, r = *(int64_t *)right;
  if ((r) < (l)) return -1;
  if ((r) > (l)) return +1;
  return 0;
}
int32_t psllcomp(const void *left, const void *right) {
  int64_t l = *(int64_t *)left, r = *(int64_t *)right;
  if ((l) < (r)) return -1;
  if ((l) > (r)) return +1;
  return 0;
}
int32_t pcharcomp(const void *left, const void *right) {
  char l = *(char *)left, r = *(char *)right;
  if ((l) < (r)) return -1;
  if ((l) > (r)) return +1;
  return 0;
}
int32_t pdoublecomp(const void *left, const void *right) {
  double l = *(double *)left, r = *(double *)right;
  if ((l) < (r)) return -1;
  if ((l) > (r)) return +1;
  return 0;
}
int32_t pstrcomp(const void *left, const void *right) {
  char *l = *(char **)left;
  char *r = *(char **)right;
  return strcmp(l, r);
}
int32_t phwllABcomp(const void *left, const void *right) {
  hwll l = *(hwll *)left, r = *(hwll *)right;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  return 0;
}
int32_t phwllREVcomp(const void *left, const void *right) {
  hwll l = *(hwll *)left, r = *(hwll *)right;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  return 0;
}
int32_t ptriplecomp(const void *left, const void *right) {
  hwllc l = *(hwllc *)left, r = *(hwllc *)right;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  if ((l.c) < (r.c)) return -1;
  if ((l.c) > (r.c)) return +1;
  return 0;
}
int32_t ptripleREVcomp(const void *left, const void *right) {
  hwllc l = *(hwllc *)left, r = *(hwllc *)right;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  if ((l.c) < (r.c)) return -1;
  if ((l.c) > (r.c)) return +1;
  return 0;
}
int32_t ptripleCABcomp(const void *left, const void *right) {
  hwllc l = *(hwllc *)left, r = *(hwllc *)right;
  if ((l.c) < (r.c)) return -1;
  if ((l.c) > (r.c)) return +1;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  return 0;
}
int32_t phwrealcomp(const void *left, const void *right) {
  hwreal l = *(hwreal *)left, r = *(hwreal *)right;
  if ((l.a) < (r.a)) return -1;
  if ((l.a) > (r.a)) return +1;
  if ((l.b) < (r.b)) return -1;
  if ((l.b) > (r.b)) return +1;
  return 0;
}
int32_t pquadcomp(const void *left, const void *right) {
  linell l = *(linell *)left;
  linell r = *(linell *)right;
  int64_t ac = phwllABcomp(&(l.a), &(r.a));
  if (ac) return ac;
  int64_t bc = phwllABcomp(&(l.b), &(r.b));
  if (bc) return bc;
  return 0;
}
int32_t pfracomp(const void *left, const void *right) {
  hwllc l = *(hwllc *)left;
  hwllc r = *(hwllc *)right;
  if ((l.a * r.b) < (l.b * r.a)) return -1;
  if ((l.a * r.b) > (l.b * r.a)) return +1;
  return 0;
}
bool isinrange(int64_t left, int64_t x, int64_t right) {
  return (left <= x && x <= right);
}
bool isinrange_soft(int64_t left, int64_t x, int64_t right) {
  return (left <= x && x <= right) || (left >= x && x >= right);
}
void sw(int64_t *l, int64_t *r) {
  if (*l == *r) return;
  int64_t t = *l;
  *l = *r;
  *r = t;
}
uint64_t frac[1048576 * 3], invf[1048576 * 3];
uint64_t ncr(int64_t n, int64_t r, uint64_t m) {
  if (n < 0 || r < 0 || n < r) return 0;
  return frac[n] * (invf[r] * invf[n - r] % m) % m;
}
int64_t a[1048576 + 5];
int64_t b[1048576 + 5];
int64_t c[1048576 + 5];
int64_t d[1048576 + 5];
int64_t e[1048576 * 4];
char s[1048576 + 1];
char t[1048576 + 1];
char u[1048576 + 1];
hwll xy[1048576 + 5];
hwllc tup[1048576 + 5];
int64_t table[3005][3005];
uint64_t gin[1048576];
uint64_t cnt[3] = {0LL};
uint64_t solve() {
  int64_t i, j, ki, li;
  int64_t result = 0;
  double dresult = 0;
  int64_t maybe = 0;
  int64_t sum = 0;
  int64_t item;
  int64_t *dpcell;
  char x = 'z';
  for (i = 0; i < n; i++) {
    if (s[i] < x) x = s[i];
  }
  for (i = 0; i < n; i++) {
    putchar(x);
  }
  puts("");
  return 0;
  result = 1;
  for (i = 0; i < n * 3; i++) {
    uint64_t v;
    switch (s[i]) {
      case 'R':
        v = 0;
        break;
      case 'G':
        v = 1;
        break;
      case 'B':
        v = 2;
        break;
    }
    if (cnt[(v + 1) % 3] && cnt[(v + 2) % 3]) {
      result *= (cnt[(v + 1) % 3] * cnt[(v + 2) % 3] % 998244353);
      result %= 998244353;
      cnt[(v + 1) % 3]--;
      cnt[(v + 2) % 3]--;
    } else {
      cnt[v]++;
    }
  }
  for (i = 1; i <= n; i++) {
    result = (result * i) % 998244353;
  }
  printf("%lld\n", result);
  return 0;
success:
  puts("Yes");
  return 0;
fail:
  puts("-1");
  return 1;
}
int32_t main(int argc, char *argv[]) {
  int32_t i, j;
  n = 4;
  m = 0;
  scanf("%llu", &n, &m);
  scanf("%llu", &k, &n, &m);
  scanf("%s", s);
  for (i = 0; i < 0; i++) {
    scanf("%lld", &a[i]);
  }
  solve();
  return 0;
}
