#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream cin ("fact.in");
    ofstream cout ("fact.out");
    int p, n=0, cnt=0, p5=0, ca, ok=2;
    cin>>p;
    ca=p*5; n=p;
    while (ca>0)
    {
        p5+=ca/5;
        ca/=5;
    }
    while (1)
    {
        if (p5==p){ok=0; break;}
            else if (p5<p){ok=-1; break;}
            else
            {
                cnt=0; ca=p5;
                while (ca>0){cnt++; ca/=5;}
                p5-=cnt; n--;
            }
    }
    if (p==0) cout<<1;
    else
    {
        if (ok==0) cout<<n*5;
    else cout<<-1;
    }
}