#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int zero(int a)
{
    int cnt=0,p=1;
    while(a>=p)
    {
        p*=5;
        cnt+=a/p;
    }
    return cnt;
}
int cautbin(int p)
{
    int st=1,dr=5*p;
    int mij;
    int t=-1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(zero(mij)==p)
        {
            t=mij;
            dr=mij-1;
        }
        else if(zero(mij)>p)
            dr=mij-1;
        else
            st=mij+1;
    }
    return t;
}
int main()
{
    int p;
    cin >> p;
    if(p==0)
        cout << 1;
    else
        cout << cautbin(p);
    return 0;
}