#include<stdio.h>
unsigned long p,s=0;

int fact5(unsigned long n)
{
              if (n%5==0) return 1+fact5(n/5);
              return 1;
}

int main()
{
    unsigned long i;
    FILE *f=fopen("fact.in","r");
    FILE *g=fopen("fact.out","w");
    fscanf(f,"%lu",&p);
    fclose(f);
    for(i=1;s<p;++i)
            s+=fact5(i);
    if (s==p) fprintf(g,"%lu",5*i-5);
       else fprintf(g,"-1");
    return 0;
}