#include <iostream>
#include <math.h>
#include <stdio.h>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long n=5,p;
long long  f(long long n) {
int i=1,s=0;
while (n/pow(5,i)) {
    s+=n/pow(5,i);
    i++;
}
return s;
}
long long factorial (long long n,long long p) {
    if (f(n)==p) return n;
    else return factorial(n+1,p);
}
int main()
{
    fin>>p;
    fout<<factorial(5,p);
    return 0;
}