Consider the regression model $y_{i}=\beta_{0}+i\beta_{1}+\epsilon_{i} (i=1,2,...,n>2)$ where $\beta_{0}$ and $\beta_{1}$ are unknown parameters and $\epsilon_{i}$ are random errors. Let $y_{i}$ be the observed value of $Y_{i}(i=1,2,...,n)$. Using the method of ordinary least squares, the estimate of $\beta_{1}$ is