#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    int p,fact=1,ok=1,n=1;
    ifstream f("fact.in");
    f>>p;
    while (ok==1)
    {
        fact=fact*n;
        if(p==0) ok=0;
        if(fact%10==0)
        {
            p=p-1;
            fact=fact/10;
            if (p==0) ok=0;
        }
        n+=1;
    }
    ofstream g("fact.out");
    g<<n-1;
    return 0;
}