#include<cstdio>
int pow5(int n)
{
    int s=0;
    long long p=5;
    while(p<=n)
      {
      s=s+n/p;
      p=p*5;
      }
    return s;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p,st=1,dr=1000000000,med,last=-1,s;
    scanf("%d",&p);
    while(st<dr)
      {
      med=(st+dr)/2;
      s=pow5(med);
      if (s>p)
          dr=med-1;
      if (s<p)
          st=med+1;
      if (s==p)
          {
          last=med;
          dr=med-1;
          }
      }
    printf("%d\n",last);
return 0;
}