#include <fstream>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");

int main() {
    int p, cinci = 0, i, iCopy;
    in >> p;

    if(p == 0)
        out << 1;
    else {
        iCopy = 5;
        for(i = 5; p >= cinci && iCopy != 1; i += 5) {
            iCopy = i;
            while(iCopy % 5 == 0) {
                cinci++;
                iCopy /= 5;
            }

            if(iCopy == 1)
                out << -1;
        }

        if(iCopy != 1)
            out << i - 5;
    }

    return 0;
}