#include <iostream>
#include <fstream>

using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
long long n,i,j,p,st,dr,m,p5[13],nr;

int main()
{
    f>>p;
    p5[0]=1;
    for(i=1;i<=11;i++)
    {
        p5[i]=p5[i-1]*5;
    }
    st=1; dr=500000001;
    while(st<=dr)
    {
        n=0;
        m=st+(dr-st)/2;
        for(i=1;i<=11;i++) nr+=m/p5[i];
        if(nr>p) dr=m-1;
        else if(nr<p) st=m+1;
        else st=dr+1, m=m-(m%5);
    }
    g<<m<<'\n';
    return 0;
}