#include <fstream>

using namespace std;

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

int zero(int x)
{
    int aux=0,aux2=5;
    while ( x>=aux2)
    {
        aux+=x/aux2;
        aux2*=5;
    }
    return aux;
}

int program(int x2)
{
    int st=1,dr=10000000,p=-1;
    while ( st<=dr)
    {
        int mij=(st+dr)/2;
        int z=zero(mij);
        if ( x2==z)
            p=mij;
        if ( x2<=z)
            dr=mij-1;
        else
            st=mij+1;
    }
    return p;
}

int main()
{
    int P;
    in>>P;
    out<<program(P);
    return 0;
}