#include <iostream>
#include<fstream>
using namespace std;

int p;


    ifstream f("fact.in");
    ofstream g("fact.out");
int fun(long long x)
{
    long long c=5,nr=0;
    while(x/c!=0)
    {
        nr=nr+x/c;
        c=c*5;
    }
    return nr;
}

int binary(long long st,long long dr)
{
    long long med=(st+dr)/2;
    long long x=fun(med);
    if(med%5==0&&x==p)
    return med;
    else
    if(x<p)
    return binary(med+1,dr);
    else
    return binary(st,med-1);
if(st>dr)
    return -1;
}

int main()
{


    long long n;
    f>>p;
    if(p==0)
        g<<1<<endl;
    else
    g<<binary(1,100000000)<<endl;
    return 0;
}