#include <cstdio>
using namespace std;
int zero(int x)
{
    int s=0,a=5;
    while(a<=x)
    {
        s+=x/a;
        a*=5;
    }
    return s;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int n=-1,p,st=0,dr=100000000,m,z;
    scanf("%d",&p);
    if(p==0)
    printf("1");
    else
    {
        while(st<=dr)
        {
            m=(st+dr)/2;
            z=zero(m);
            if(z>p)
            dr=m-1;
            if(z<p)
            st=m+1;
            if(z==p)
            n=m,dr=m-1;
        }
            printf("%d\n",n);
    }
    return 0;
}