/*Se da un numar intreg P. Sa se gaseasca cel mai mic numar natural strict 
pozitiv N pentru care N! are exact P cifre de 0 la sfarsit.

Se stie ca N! = 1 * 2 * 3 * .... * (N - 1) * N.
Exemplu : 0 --> 1
          2	--> 10
          10 --> 45*/

#include<stdio.h>
#include<stdlib.h>

const long int MAX=1000;

long n;

long factor(int m){
     if (0 == m)
        return 1;
     else
         return (m * factor(m-1));
}

long ten(long m){
    long int i=0;
    while(m>=5){
                if(m%5==0)
                          i++;
                m/=5;
                }
    return i;
}  

int fact(long a,long b,long n){
     long c=(a+b)/2;
     if(ten(factor(c))==n)
                          return c;
     else
         if(a<b)
                if(ten(factor(c))<n)
                                    fact(c+1,b,n);
                else
                    fact(a,c-1,n);
}

int main(){
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%ld",&n);
    long a=0L;long b=MAX;
    int rez=fact(a,b,n);
    if(rez)
           printf("%d",rez);
    else(printf("%d",-1));
    return 0;
}