#include <iostream>
#include <fstream>
using namespace std;
int exponent,p,n,x,y,s;
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    in>>p>>n;

    s=0;
    x=5;


    while(s<p)
    {
        exponent=0;
        y=x;
        while(y%5==0)
        {
            exponent++;
            y/=5;
        }

        s=s+exponent;

        x=x+5;
    }
    out<<x-5;
    in.close();
    out.close();

    return 0;
}