#include <iostream>
#include <fstream>

using namespace std;

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

long long p,rez=-1;
int main()
{
    f>>p;
    long long st=1,dr=1000000100,cont,mid;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        cont=0;
        for(int i=5;i<=mid;i=i*5)
        cont+=(mid/i);
        if(cont==p)
        {
            rez=mid;
            dr=mid-1;
        }
        else if(cont<p)
            {
                st=mid+1;
            }
            else if(cont>p)
                {
                    dr=mid-1;
                }
    }
    g<<rez;
}