#include<cstdio>
const int inf=2147483647;
int main()
{
 freopen("fact.in","r",stdin);
 freopen("fact.out","w",stdout);
 int p;
 scanf("%d ",&p);
 int st=0,dr=inf,mij,rasp=-1;
 while(st<=dr)
       {
        mij=(st+dr)/2;
        int p5=0,a5=5;
        while(mij/a5!=0)
              {
               p5+=mij/a5;
               a5*=5;
              }
        if(p5>=p)
           {
            dr=mij-1;
            if(p5==p)
               rasp=mij;
           }
        else
           st=mij+1;
       }
 printf("%d\n",rasp);
 return 0;
}