#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout ("fact.out");
int n,p,z[30],a[30],i;
int main()
{
    fin>>p;
    if(p==0) {fout<<1; return 0;}
    if(p==5) {fout<<-1; return 0;}
    if(p==1) {fout<<5; return 0;}
    a[1]=5;
    z[1]=1;
    n=1;
    while(z[n]+a[n]<p)
    {
        n++;
        z[n]=z[n-1]+a[n-1];
        a[n]=a[n-1]*5;
    }

    if(z[n]+a[n]==p) {fout<<n; return 0;}

    return 0;
}