#include <fstream>
#include <iostream>
#define ll long long
	
using namespace std;
	
	
ifstream in("fact.in");	
ofstream out("fact.out");	 
	
int zero(ll n) {
    ll nrz = 0;
    for(ll d = 5; d <= n; d *= 5) {
        nrz += n / d;
    }
    return nrz;
}

int main() {	
	
    ll  p;
    ll s = 1, d = 100000000;
    in >> p;
    
    while(s <= d) {
        ll m = (s + d) / 2;
        if(zero(m) < p) {
            s = m + 1;
        }
        else {
            d = m - 1;
        }
    }
    if(zero(s) == p) 
        out << s;
    else
        out << -1;
    return 0;	
}