#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("factorial.in");
ofstream fout("factorial.out");
int num,stanga,dreapta;

int main()
{
    fin>>num;
    stanga=1;
    dreapta=num*5;
    while (stanga<=dreapta)
    {
        int mijloc=(stanga+dreapta)/2;
        int nr=mijloc;
        int solutie=0;
        int m=5;
        while (nr>=m)
        {
            solutie+=nr/m;
            m*=5;
        }
        if (solutie>=num)
        {
            dreapta=mijloc-1;
        }
        else
        {
            stanga=mijloc+1;
        }
    }
    fout<<stanga;
    return 0;

}