#include <bits/stdc++.h>
using namespace std;
long long powmod(long long a, long long b) {
  long long res = 1;
  a %= 1000000007;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % 1000000007;
    a = a * a % 1000000007;
  }
  return res;
}
template <typename T>
inline bool chkmin(T &a, const T &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T>
inline bool chkmax(T &a, const T &b) {
  return a < b ? a = b, 1 : 0;
}
int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
const int P = 10000007;
unsigned int p[500100], l[500100], r[500100];
int m;
char ans[500100], s[500100];
int n;
bool ok(int i, int x) {
  if (++i < x) return 0;
  return ((r[i] - r[i - x] * p[x]) * p[i - x]) == (l[i] - l[i - x]);
}
bool dfs(int i, int x) {
  if (i == n) {
    puts(ans);
    return 1;
  }
  ans[i] = x ? s[i] : 'a';
  for (; ans[i] <= 'z'; ans[i]++) {
    l[i + 1] = l[i] + ans[i] * p[i];
    r[i + 1] = r[i] * P + ans[i];
    if (!ok(i, m) && !ok(i, m + 1) && dfs(i + 1, x && (ans[i] == s[i])))
      return 1;
  }
  return 0;
}
int main() {
  m = read();
  scanf("%s", s);
  n = strlen(s);
  int i;
  for (i = n - 1; i >= 0 && s[i] == 'z'; i--) s[i] = 'a';
  if (i == -1) {
    puts("Impossible");
    return 0;
  }
  s[i]++;
  p[0] = 1;
  for (int i = 1; i < 500100; i++) p[i] = p[i - 1] * P;
  if (!dfs(0, 1)) puts("Impossible");
  return 0;
}
