#include <bits/stdc++.h>
using namespace std;
const int lim = 1e6 + 1;
int criba[lim];
void fun_criba(int n) {
  for (int i = 2; i <= 2; i++) {
    if (criba[i] == 0)
      for (int j = i + i; j <= n; j += i) {
        criba[j] = i;
      }
  }
  for (int i = 3; i <= n; i += 2) {
    if (criba[i] == 0)
      for (int j = i + i; j <= n; j += i) {
        criba[j] = i;
      }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int x;
  cin >> x;
  memset(criba, 0, sizeof criba);
  fun_criba(x);
  int a = x;
  int num = x;
  for (int i = x - criba[x] + 1; i < x; i++) {
    if (a >= (i - criba[i])) {
      a = i - criba[i];
      num = i;
    }
  }
  x = num;
  if (criba[x] != 0)
    num = x - criba[x] + 1;
  else
    num = x - criba[x];
  cout << num;
  return 0;
}
