#include <iostream>
#include <fstream>

using namespace std;

int f(int n){
    int rez=0;
    for(int i=5;i<=n;i*=5)
        rez+=n/i;

    return rez;
}


int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");

    int p;
    in>>p;
    int s=1, d=p*5, nr;
    while (s<=d){
        nr= (s+d)/2;
        if (f (nr) >= p )
            d=nr-1;
        else
            s=nr+1;
    }

    if ( f(s) == p )
        out<<s;
    else
        out<<-1;
    in.close();
    out.close();
    return 0;
}