#include <iostream>
#include <fstream>
#define NMAX 10000000001

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int ans,nr,ok;
unsigned long long p,i;
int factorial(int number)
{
    unsigned long long  f=5;
    int sum=0;
    while(number/f>0)
    {
        sum=number/f;
        f*=5;
    }
    return sum;
}
int main()
{
    fin>>p;
    for(i =1 ; i <= NMAX; i++)
    {
        ans=factorial(i);
        if(ans==p)
        {
            ok=1;
            fout<<i;
            break;
        }
    }
    if(!ok) fout<<-1;
    return 0;
}