#include <iostream>
#include <fstream>
#include <stdio.h>
#include <math.h>

using namespace std;
int p;

int hanynulla(int n)
{
    int ok=0;
    while(n != 0)
    {
        ok=ok + n/5;
        n /=5;
    }
    if(ok < p) return 1;
    else return 0;
}
int binker(int a, int b, int x)
{
    int k=(a+b)/2;
    if(a==b)return a;
    else if(hanynulla(k))return binker(k+1,b,x);
    else return binker(a,k,x);
}

int main()
{

    ifstream be("fact.in");
    be>>p;
    ofstream ki("fact.out");
    int a,b;
    if(p==0)ki<<1;
    else ki << binker(1,100000000,p);

    return 0;
}