#include <fstream>
using namespace std;
int zero(int x)
{
    int nr=0;
    if(x%10==0)
    {
        nr++;
        x=x/10;
    }
    return nr;
}
int main()
{
    int s=1,k=2,i,p;
    ifstream cin ("fact.in");
    ofstream cout ("fact.out");
    cin>>p;
    if(!p)
        cout<<0;
    else
    while(zero(s)!=p)
    {
        s=s*k;
        k++;
    }
    cout<<k;
    return 0;
}