#include <cstdio>
int ls,ld,mij,p,n=-1,i,k;
int main(){
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    ls=1;ld=1<<30;
    while (ls<=ld){
          mij=(ls+ld)/2;
          for (i=5,k=0;i<=mij;i*=5) k+=(mij/i);
          if (k==p) n=mij;
          if (k>=p) ld=mij-1;
                else ls=mij+1;
          }
    printf("%d",n);
    return 0;
}