#include <fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");

long long  f(long long n)
{
    long long sol=0;
    while(n>0)
    {
        sol+=n/5;
        n/=5;
    }
    return sol;
}
int main()
{
    long long n,r=0,pas=1<<60;
    cin>>n;
    while(pas)
    {
        if(f(r+pas)<n)
            r+=pas;
        pas/=2;
    }
    if(f(r+1)==n)
        cout<<r+1;
    else
        cout<<-1;
    return 0;
}