#include<stdio.h>

FILE *f, *g;

long p, i, j, t, y, s, s2, o, o2;

int main()
{
    f=fopen("fact.in", "r");
    g=fopen("fact.out", "w");
    fscanf(f, "%ld", &p);

    i=10;
    while(1)
    {
    t=5;
    y=2;
    o=0;
    o2=0;
    do
    {
        s=i/t;
        o+=s;
        t*=t;

    }
    while(s);
    do
    {
        s2=i/y;
        o2+=s2;
        y*=y;
    }
    while(s2);
    if(o2>=o && o==p)
    {
        fprintf(g, "%ld", i);
        break;
    }
    else if(o2>=o && o>p)
    {
        fprintf(g, "-1");
        break;
    }
     i++;
    }
   fclose(f);
   fclose(g);
   return 0;
}