#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int factorial(int x)
{
    int i,nr=0;
    for(i=5;i<=x;i*=5)
        nr+=x/i;
    return nr;
}
int main()
{
    int p;
    fin >> p;
    int a=1,b=p*5,c;
    while(a<=b)
        {
            c=(a+b)/2;
            if(factorial(c)>=p)
                b=c-1;
            else
                a=c+1;
        }
    if(factorial(a)==p)
        {
        fout << a << "\n";
        }
    else
        fout << -1 << "\n";
    return 0;
}