#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long mij,a,b,y,nr5,p;
int main()
{
    fin>>p;
    a=1;b=2000000000;
    while(a<=b)
    {
        mij=(a+b)/2;
        nr5=0;
        y=5;
        while(y<=mij)
        {
            nr5=nr5+mij/y;
            y=y*5;
        }
        if(nr5==p)
            break;
        else
            if(nr5<p)
            a=mij+1;
        else
            b=mij-1;

    }
    mij=mij-mij%5;
    fout<<mij;
    return 0;
}