I use long long int with MinGW and have right answer for the input of 1000000000.Why it is still wrong?
Here is my C code.
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int sum(int a);
int main()
{
    int count[10],i,j,base=0;        //use count[2] to count [9] to store the number of digits
    long long int n,product=0;
    for(i=0;i<10;i++)
        count[i]=0;
    scanf("%lld",&n);
    if(n==1)
        printf("%d\n",1);
    else if(n==0)
        printf("%d\n",10);
    else{
    for(i=9;i>1;i--){
        while(n%i==0){
            n/=i;
            count[i]++;
        }
    }
    if(n==1){
  /*      for(i=2;i<=9;i++){
            for(j=0;j<count[i];j++){
                printf("%d",i);
            }
        }
  */
        for(i=9;i>=2;i--){
            product=product+i*sum(count[i])*pow(10,base);
            base=base+count[i];
        }
        printf("%lld",product);
    }
    else
        printf("%d",-1);
    printf("\n");
    }
    system("pause");
    return 0;
}

int sum(int a)
{
    int term=1,i,result=0;
    for(i=0;i<a;i++){
        result+=term;
        term*=10;
    }
    return result;
}