#include<iostream>
#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
    int n,p,i,s,z;
    s=1;
    n=0;
    in>>p;
    z=p;
    for(i=1;i<=99;i++)
    {
        s=s*i;
        if(s%10==0)
        {
        s=s/10;
        z=z-1;

        if(z==0)
        {
            n=i;
            break;
        }
        }
    }
    if(n==0)
        n=1;
    out<<n;
    return 0;
}