#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
    {
        for(i = 1; p != cinci; i++) {
            iCopy = i;
            while(iCopy % 5 == 0) {
                cinci++;
                iCopy /= 5;
            }
        }

        out << i - 1;
    }

    return 0;
}