#include <iostream>
#include <fstream>

using namespace std;

ifstream in  ("fact.in" );
ofstream out ("fact.out");

int zero (int mid)
{
    int z=5,nr=0;
    while (z<=mid)
    {
        nr+=mid/z;
        z*=5;
    }
    return nr;
}
 
int main()
{
	long p;
    in>>p; 
    in.close();
	
	long long start=1;
	long long end=2000000001;
	long long mid;
	long long int nr=-1;
	long long aux;
    while (start<=end)
    {
        mid=(start+end)/2;
        
         aux=zero(mid);
         
        if (aux<p)
            start=mid+1;
        else    
        if (aux>p)
            end=mid-1;
            
        if (aux==p)
        {
            nr=mid;
			end=mid-1;
        }
    }
    
    out<<nr;
    out.close();
    return 0;
}