#include <fstream>
#include <cmath>
using namespace std;
 
int findN(int p) {
    int i = 0;
    int exp;

    if (p == 0)
        return 1;

    while (p > 0) {
        i = i + 5;
        exp = (int)(log(i) / log(5));
        if (pow(5, exp) == i)
            p = p - exp;
        else if (i % 25 == 0)
            p = p - 2;
        else p--;
    }

    if (p < 0)
        return -1;

    return i;
}

int main() {
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    int p;
    fin>>p;
    fout<<findN(p);
    return 0;
}