#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int p,n,c,s,i;
    f>>p;
    c=1;
    n=0;
    s=1;
    for(i=1;i<=p;i++)
    {
        c=c*10;
    }

    while(s%c!=0)
    {
        n=n+1;
        s=s*n;
    }

    g<<n;
    return 0;
}