#include<fstream>
using namespace std;

ifstream cin("fact.in");
ofstream cout("fact.out");

long long z(long long n)
{
    long long count = 0;
    for (long long i = 5; n / i >= 1; i *= 5)
        count += n / i;

    return count;
}
int main()
{
    long long jump = 1LL << 60;
    long long ans = 0,p; cin >> p;
    while(jump)
        {
            if(z(ans + jump) < p) ans += jump;
            jump >>= 1;
        }

    int rez = z(ans + 1) == p ?  ans + 1 : -1;
    cout << rez;

}