View Compilation Error

0_0_28554021_17554.cpp: In function 'int main()':
0_0_28554021_17554.cpp:25:13: error: expected ';' before 'if'
             if((t2-t1-1)*b>2*a)  res+=2*a+b;
             ^
0_0_28554021_17554.cpp:26:13: error: 'else' without a previous 'if'
             else  res+=b*(t2-t1);
             ^