#include <cstdio>
#include <fstream>
using namespace std;
const long long NMAX=1e7;
long long n0(long long n)
{
    long long p=5,ex=0;
    while(p<=n)
    {
        ex+=n/p;
        p*=5;
    }
    return ex;
}
int main()
{
    freopen("factorial.in","r",stdin);
    freopen("factorial.out","w",stdout);
    long long n,st,dr,med,ans=-1,a;
    scanf("%lld",&n);
    st=1;dr=NMAX;
    while(st<=dr)
    {
        med=(st+dr)/2;
        a=n0(med);
        if(a==n)
        {
            ans=med;
            dr=med-1;
        }
        else
            if(a>n)
                dr=med-1;
            else
                st=med+1;
    }
    printf("%lld",ans);
    return 0;
}