#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("factorial.in");
ofstream g ("factorial.out");
long long n,p,ls,ld;
int nz (int n)
{
    int k=n,p=5;
    while (p<=n)
    {
        k+=n/p;
        p=p*5;
    }
    return k;
}

int main()
{
    f>>p;
    ls=1;
    ld=1000000000;
    int sw=0;
    while (ls<=ld&&!sw)
    {
        if (p>nz((ls+ld)/2)) ls=(ls+ld)/2+1;
        else if (p<nz((ls+ld)/2)) ld=(ls+ld)/2-1;
        else
        {
            g<<((ls+ld)/2)*5;
            sw=1;
        }
    }
    if (sw==0) g<<(ls+ld)/2*5+5;
    return 0;
}