#include <stdio.h>
#include <stdlib.h>
long long legendre(long long n,long long x)
{
    long long z=0,b;
    b=x;
    while(b<=n)
    {
        z+=(n/b);
        b*=x;
    }
    return z;
}
int main()
{
    long long p,i,pas,x;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%lld",&p);
    i=0;
    pas=1<<30;
    while(pas!=0)
    {
        if(legendre(i+pas,5)<p)
            i+=pas;
        pas/=2;
    }
    if(legendre(i+1,5)==p)
        printf("%d\n",i+1);
    if(legendre(i+1,5)>p)
        printf("%d\n",-1);

    return 0;
}