sees A and B are solving the following equations: \begin{cases}\begin{array}\\ x+ y=2536\\x+y=704\end{array}\end{cases }, where the coefficients in front of the unknown are covered by A and B. A calculates that the solution of the equation is x=7, y=3; while B mistakenly regards "2536" as "1536", the solution obtained is x=4, y=4. Ask: What is the smallest of the four covered coefficients in the equation system? □
丙看到甲、乙两人正在解下面这个方程组：\begin{cases}\begin{array}\\□x+□y=2536\\□x+□y=704\end{array}\end{cases}，其中未知数前面的系数被甲和乙遮住了．甲计算得出方程的解是x=7，y=3；而乙误把"2536"看作"1536"，得到的解是x=4，y=4．试问：方程组四个被遮住的系数中最小的一个是多少？□
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