#include <fstream>
using namespace std;
unsigned long long p;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long long fact(unsigned long long n)
{
    unsigned long long factorial=1;
    if(n==0||n==1)
    return 1;
    else{
   for(unsigned long long i=2;i<=n;i++)
   factorial=factorial*i;

    }
   return factorial;
}
unsigned long long zerouri(unsigned long long n)
{
    int d10=0;
    while (n % 10== 0) {
            n /= 10;
            d10++;
        }
        return d10;
}
int main()
{
    f>>p;
   unsigned long long i=1;
    int ok=0;
         while(zerouri(fact(i))!=p)
         {
         i++;
    }
     g<<i;
    return 0;
}