#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int pow_5(int n)
{
    int count=0;
    while(n%5==0)
    {
        n/=5;
        count++;
    }
    return count;
}
int no_0(int n)
{
    int k=0;
    for(int i = 1; i <= n; i++)
    {
        k+=pow_5(i);
    }
    return k;
}
int main()
{
    int p;
    in>>p;
    int r = -1;
    int st = 0;
    unsigned int dr = 4294967295;
    int q;
    while(st < dr)
    {
        q = (st+dr)/2;
        if(no_0(q)==p)
        {
            r = q;
            break;
        }
        else if(no_0(q) < p) st = q + 1;
        else dr=q-1;
    }
        for(int i = 3; i>=0; i--)
        {
            if(r%5==0)break;
            r--;
        }
    out<<r;
    return 0;
}