#include <cstdio>
using namespace std;
int p;
int zero(int x)
{
    int s=0,num=5;
    while (x/num>0)
    {
        s=s+x/num;
        num=num*5;
    }
    return s;
}
int bs_left(int st,int dr)
{
    int med,last=-1;
    while (st<=dr)
    {
        med=st+(dr-st)/2;
        if (p<=zero(med))
        {
            last=med;
            dr=med-1;
        }
        else
            st=med+1;
    }
    return last;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    printf("%d",bs_left(1,1000000000));
    return 0;
}