#include <stdio.h>

const int nmax=500000000;

int nzero(int x)
{
    int ans=0;
    while (x > 0)
    {
        x/=5;
        ans+=x;
    }
    return ans;
}

int bin_search(int n, int p)
{
    int s,d,m,x,ans;

    s=1;
    d=n;
    ans=-1;
    while (s <= d)
    {
        m=s+(d-s)/2;
        x=nzero(m);

        if (p > x)
            s=m+1;
        else
        {
            if (x == p)
                ans=m;
            d=m-1;
        }

    }
    return ans;
}

int main()
{
    int p;
    FILE *f;

    f=fopen("fact.in","r");
    fscanf(f,"%d",&p);
    fclose(f);

    f=fopen("fact.out","w");
    if (p == 0)
        fprintf(f,"1");
    else
        fprintf(f,"%d",bin_search(nmax,p));
    fclose(f);
}