#include <iostream>
#include <fstream>

using namespace std;

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

long long sum[1001],P,S=1,n,s;
const long long N=1<<20;

int caut()
{
    long long pas=N;
    int r=0;
    while(pas!=0)
    {
        if(pas+r<=n && sum[pas+r]<=P)
        {
            r+=pas;
        }
        pas/=2;
    }
    return r;
}

int main()
{
    int i=1,nr=0;
    in>>P;
    sum[0]=1;
    n++;
    if(P==1)
        out<<0;
    else
    {
        while(nr<P)
        {
            S=S*i;
            while(S%10==0)
            {
                nr++;
                S=S/10;
            }

            sum[i]=nr;
            n++;
            i++;
        }
        out<<caut();
    }
    return 0;
}