Find the output of the following program 

    #include iostream
    #include cstring
    using namespace std;
    int main ()
    {
        char str1[10] = "Hello";
        char str2[10] = "World";
        char str3[10];
        int  len ;
        strcpy( str3, str1);
        strcat( str1, str2);
        len = strlen(str1);
        cout  len  endl;
        return 0;
    }