#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out")
long long int legendre(long long int x)
{
    long long int sum=0;
    x/=5;
    while (x>0)
    {
        sum+=x;
        x/=5;
    }
    return sum;
}

int main()
{
    long long int prev=1,next=100000000,mid;
    long long int p;
    cin >> p;
    while (prev<next)
    {
        mid=(prev+next)/2;
        if(legendre(mid)==p && legendre(mid-1)!=p)
            break;
        if(legendre(mid)<p)
            prev=mid;
        else
                next=mid;
    }
    if(legendre(prev)==p)
        mid=prev;
    cout << mid;
    return 0;
}