#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int main()
{
    long long contor=0, fact=1, p, n=1;
    cin>>p;
    while(contor<p)
    {
       fact=fact*n;
       while(fact%10==0)
       {
       contor++;
       fact=fact/10;
       }
       fact=fact %10;
       n++;
    }
    cout<<n-1;
    return 0;
}