#include <fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int f(int n)
{
    int p=5,s=0;
    while(p<=n)
    {
        s=s+n/p;
        p=p*5;
    }
    return s;
}
int main()
{
    int n,i=1;
    bool ok=0;
    cin>>n;
    while(ok<1)
    {
        if(f(i)==n)
            break;
        i++;
    }
    cout<<i;
    cin.close();
    cout.close();
    return 0;
}