#include<stdio.h>
 
long v[1000000];
long val(long a)
{
    long s=0;
    while(a>0)
        {
        s+=a/5;
        a/=5;
        }
    return s;
}
 
long cauta(int a,int b,int n)
{
    long c,t;
    c=(a+b)/2;
    t=val(c);
    if(a==b && t==n ) return b;
    if(a==b) return -1;
     
     
    if(t>=n) return cauta(a,c,n);
    else return cauta(c+1,b,n);
 
}
 
int main()
{
    freopen("fact.in","rt",stdin);
    freopen("fact.out","wt",stdout);
    long N;
    scanf("%ld",&N);
    printf("%ld",cauta(1,500000000,N));
     
     
    return 0;
}