#include<fstream>
using namespace std;
int main()
{
    ifstream fin ("fact.in");
    ofstream fout("fact.out");
    int n,p,x,y;
    fin>>p;
    for(n=1;n++;)
    {
        x=0;
        y=5;
        while(y<=n)
        {
            x=x+(n/y);
            y=y*5;
        }
        if(x==p)
        {fout<<n;
        return 0;
        }
    }
    fout<<"-1";
    fin.close();
    fout.close();

}