Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
|  |  | Year ended December 31, | Year ended December 31, | Year ended December 31, | Year ended December 31, | Year ended December 31, |
| --- | --- | --- | --- | --- | --- | --- |
|  |  | 2017 | 2016 | 2015 | 2014 | 2013 |
| Financial Data (in millions, except per share amounts): | Operating revenues | $21,171 | $20,425 | $19,820 | $18,605 | $17,699 |
| Financial Data (in millions, except per share amounts): | Operating expenses | 17,656 | 16,665 | 15,704 | 16,380 | 16,421 |
| Financial Data (in millions, except per share amounts): | Operating income | 3,515 | 3,760 | 4,116 | 2,225 | 1,278 |
| Financial Data (in millions, except per share amounts): | Other expenses (income) net | 264 | 213 | 637 | 409 | 69 |
| Financial Data (in millions, except per share amounts): | Income before taxes | 3,251 | 3,547 | 3,479 | 1,816 | 1,209 |
| Financial Data (in millions, except per share amounts): | Provision for income taxes | (237) | 1,303 | 1,298 | 680 | 455 |
| Financial Data (in millions, except per share amounts): | Net income | $3,488 | $2,244 | $2,181 | $1,136 | $754 |
| Financial Data (in millions, except per share amounts): | Net income per share, basic | $5.80 | $3.58 | $3.30 | $1.65 | $1.06 |
| Financial Data (in millions, except per share amounts): | Net income per share, diluted | $5.79 | $3.55 | $3.27 | $1.64 | $1.05 |
| Financial Data (in millions, except per share amounts): | Cash dividends per common share | $0.4750 | $0.3750 | $0.2850 | $0.2200 | $0.1300 |
| Financial Data (in millions, except per share amounts): | Total assets at period-end | $25,110 | $23,286 | $21,312 | $19,723 | $19,177 |
| Financial Data (in millions, except per share amounts): | Long-term obligations at period-end | $3,320 | $2,821 | $2,541 | $2,434 | $2,191 |
| Financial Data (in millions, except per share amounts): | Stockholders’ equity at period-end | $10,430 | $8,441 | $7,358 | $6,775 | $7,336 |
| Operating Data: | Revenue passengers carried | 130,256,190 | 124,719,765 | 118,171,211 | 110,496,912 | 108,075,976 |
| Operating Data: | Enplaned passengers | 157,677,218 | 151,740,357 | 144,574,882 | 135,767,188 | 133,155,030 |
| Operating Data: | Revenue passenger miles (RPMs) (000s) (a) | 129,041,420 | 124,797,986 | 117,499,879 | 108,035,133 | 104,348,216 |
| Operating Data: | Available seat miles (ASMs) (000s) (b) | 153,811,072 | 148,522,051 | 140,501,409 | 131,003,957 | 130,344,072 |
| Operating Data: | Load factor (c) | 83.9% | 84.0% | 83.6% | 82.5% | 80.1% |
| Operating Data: | Average length of passenger haul (miles) | 991 | 1,001 | 994 | 978 | 966 |
| Operating Data: | Average aircraft stage length (miles) | 754 | 760 | 750 | 721 | 703 |
| Operating Data: | Trips flown | 1,347,893 | 1,311,149 | 1,267,358 | 1,255,502 | 1,312,785 |
| Operating Data: | Seats flown (d) | 200,878,967 | 193,167,695 | 184,955,094 | 179,733,055 | 183,563,527 |
| Operating Data: | Seats per trip (e) | 149.03 | 147.33 | 145.94 | 143.16 | 139.83 |
| Operating Data: | Average passenger fare (j) | $146.95 | $149.09 | $154.85 | $159.80 | $154.72 |
| Operating Data: | Passenger revenue yield per RPM (cents) (f)(j) | 14.83 | 14.90 | 15.57 | 16.34 | 16.02 |
| Operating Data: | Operating revenue per ASM (cents) (g) | 13.76 | 13.75 | 13.98 | 14.20 | 13.58 |
| Operating Data: | Passenger revenue per ASM (cents) (h)(j) | 12.44 | 12.52 | 13.02 | 13.48 | 12.83 |
| Operating Data: | Operating expenses per ASM (cents) (i) | 11.48 | 11.22 | 11.18 | 12.50 | 12.60 |
| Operating Data: | Operating expenses per ASM, excluding fuel (cents) | 8.92 | 8.76 | 8.60 | 8.46 | 8.18 |
| Operating Data: | Operating expenses per ASM, excluding fuel and profitsharing (cents) | 8.56 | 8.37 | 8.16 | 8.19 | 8.01 |
| Operating Data: | Fuel costs per gallon, including fuel tax | $1.92 | $1.82 | $1.90 | $2.93 | $3.16 |
| Operating Data: | Fuel costs per gallon, including fuel tax, economic | $2.00 | $1.92 | $2.07 | $2.92 | $3.12 |
| Operating Data: | Fuel consumed, in gallons (millions) | 2,045 | 1,996 | 1,901 | 1,801 | 1,818 |
| Operating Data: | Active fulltime equivalent Employees | 56,110 | 53,536 | 49,583 | 46,278 | 44,381 |
| Operating Data: | Aircraft at end of period | 706 | 723 | 704 | 665 | 681 |
Question:
How many planes did Southwest own in 2013?
Answer:
681