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

int main()
{
int P,N=1,nr5=0,CN=1;
ifstream fin("fact.in");
ofstream fout("fact.out");
fin>>P;
if(P==0)
{
    fout<<1;
    return 0;
}
while(P>nr5)
{
    N++;
    CN=N;
    while(CN%5==0)
    {
        nr5++;
        CN=CN/5;
    }
}
if(P==nr5)
    fout<<N;
else
    fout<<-1;
return 0;
}