#include <stdio.h>
#include <stdlib.h>
int legendre(int x)
{
    int p5=5,nr=0;
    while(p5<=x)
    {
        nr+=(x/p5);
        p5*=5;
    }
    return nr;
}
int cautbin(int p)
{
    int i=0,pas=1<<30;
    while(pas)
    {
        if(legendre(i+pas)<p)
            i+=pas;
        pas/=2;
    }
    if(legendre(i+1)==p) return i+1;
    else return -1;
}
int main()
{
    int p;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    printf("%d\n",cautbin(p));

    return 0;
}