#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("fact.in");
ofstream fout ("fact.out");
int main()
{
    long long int suma,numar,termen=5,st=1,dr=2e9,mij,poz=2e9,P;
    fin>>P;

        while(st<=dr)
        {
            mij=(st+dr)/2;
            termen=5;
            suma=0;
            numar=mij;
            while(termen<=numar)
            {
                suma=suma+numar/termen;
                termen=termen*5;
            }
            if(suma>=P)
            {
                poz=min(poz,mij);
                dr=mij-1;
            }
            else
                st=mij+1;
        }
        fout<<poz;

    return 0;
}