#include <iostream>
#include <cstdio>
#define nmax 1000000000
FILE * f = fopen("fact.in", "r");
FILE * g = fopen("fact.out", "w");
using namespace std;
int p;
int factorial (int h) {
    int p = 1, h1, s = 0;
    h1 = h;
    while (p < h)
    {
        p = p * 5;
        s = s + h1/p;
    }
    return s;
}
int main()
{ int ok = 0, q = 0, i;
    fscanf(f,"%d",&p);
    for(i=5;i<=nmax && ok == 0;i+=5)
    {
        if(factorial(i) == p)
        {
            q = i;
            ok = 1;
        }
    }
    fprintf(g,"%d",q);
    fclose(f);
    fclose(g);
    return 0;
}