#include<iostream>
#include<fstream>
using namespace std;
ifstream in("factorial.in");
ofstream out("factorial.out");
int main()
{
    int n,p,i,s,z;
    n=0;
    in>>p;
    z=p;
    for(i=1;i<=n;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;

    cout<<"n="<<n;

    return 0;
}