#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long numar(long long x){
    long long nr=0,y=5;
    while(x>=y)
    {
        nr+=x/y;
        y*=5;
    }
    return nr;
}
long long caut(long long a, long long b, long long x){
    long long k;
    long long m;
    while (a < b) {
        m = (a + b) / 2;
        k=numar(m);
        if (k < x)
            a = m + 1;
        else
            b = m;
    }
    m = (a + b) / 2;
    k=numar(m);
    if (k < x) m ++;
        return m;
}
int main()
{
    long long n,k;
    f>>n;
    k=caut(1,1844674407370954354,n);
    g<<k;
    return 0;
}