"123 35   123 0    0      0       817 0    0   0   0"

int a, b, c;
if( sscanf(string, "%d %d %d", &a, &b, &c) == 3)
  printf("the third number is %dn", c);

int a;
if( sscanf(string, "%*d %*d %d", &a) == 1)
  printf("the third number is %dn", a);

const char *input = "...";
int value;

// here we use the '*' modifier to discard the input from our string
sscanf("%*i %*i %i", &value);

// value now magically has the value you need.