#include <bits/stdc++.h>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long long mij,p,st,dr;
int nr_zero(int val)
{
    int p=5,nr=0;
    while(p<=val)
    {
        nr=nr+val/p;
        p=p*5;
    }
    return nr;
}
int main()
{
    f>>p;
    st=1;
    dr=5*p;
    mij=1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(nr_zero(mij)>=p)
        {
            dr=mij-1;
        }
        else st=mij+1;
    }
    g<<mij<<'\n';
    return 0;
}