给出一个等差数列的前两项a1a_1a1，a2a_2a2，求第nnn项是多少。
一行，包含三个整数a1a_1a1，a2a_2a2，nnn。−100≤a1−100≤a_1−100≤a1,a2≤100a_2≤100a2≤100，0<n≤10000< n ≤ 10000<n≤1000。
一个整数，即第nnn项的值。
1 4 100
298
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