#include <iostream>
#include <fstream>

using namespace std;

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

int p;

int count0(int n)
{
    int s=0,p=5;
    while(p<=n)
    {
        s=s+n/p;
        p=p*5;
    }
    return s;
}

int cautbin(int x)
{
    int st=1,dr=1000000005;
    bool ok=false;
    int mij,a,ind=0;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        a=count0(mij);
        if(a>=x)
        {
            ind=mij;
            dr=mij-1;
            if(a==x)
                ok=true;
        }
        else
            st=mij+1;
    }
    if(ok)
        return ind;
    return -1;
}
int main()
{
    fin>>p;
    fout <<cautbin(p)<<"\n";
    return 0;
}