#include <iostream>

#include <fstream>

using namespace std;

int nzero(int n)
{
    int nr5=0;
    while(n>=5)
    {
        nr5+=n/5;
        n=n/5;
    }
    return  nr5;
}

int main()
{
    int p, n,i,pr=1;
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    cin>>p;
    n=0;
    while(p!=nzero(n))
    {
        n++;
    }
    if(p!=0)
    cout<<n;
    else cout<<1;


    return 0;
}