#include <fstream>

using namespace std;

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    int p,cnt=0,cf,cnt2=0,i=1;
    long long f = 1;
    cin >> p;
    for(int i = 1; i <= 200000000; i++)
    {
      cnt = 0;
      f = f * i;
      cnt2++;
      cf = f;
      while(cf > 0)
      {
        if(cf % 10 == 0)
          cnt++;
        else
          break;
        cf /= 10;
      }
      if(cnt >= p)
        break;
    }
    cout << cnt2;
    return 0;
}