#include <fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");
    int P;
void factorial()
{
    long double nr=1;
    long long int aux;
    unsigned int b=0;
    for(long long int i=1;i<=25;i++){b=0;
                                     nr=nr*i;
                                     aux=(long long int)nr%100000000;
                                     while(aux%10==0){b++;
                                                      aux=aux/10;}
                                     if(b==P){out<<i;
                                              break;}}
}
    
int main()
{
    in>>P;
    factorial();
    return 0;
}