#include <fstream>

using namespace std;

long zerouri(long n,int power)
{
    if(n==0) return 0;
    else return n/power+zerouri(n/power,power*5);
}

int main()
{
    fstream f("fact.in",ios::in);
    long p;
    f>>p;
    f.close();
    f.open("fact.out",ios::out);
    for(long i=1;i<=100000000;i++)
    {
        if(zerouri(i,5)==p)
        {
            f<<i;
            break;
        }
    }
    //long z=zerouri(p,5);
    //f<<z;
    f.close();
    return 0;
}