golang

// script.go
package main

import (
    "fmt"
    "os"
)

func main() {
    var N, V int
    fmt.Fscanln(os.Stdin, &N, &V)
    vw := make([][]int, N)
    for i := range vw {
        var v, w int
        fmt.Fscanln(os.Stdin, &v, &w)
        vw[i] = []int{v, w}
    }
    fmt.Println(backpack(vw, N, V))
}

func backpack(vw [][]int, N int, V int) int {
    dp := make([][]int, N+1)
    for i := range dp {
        dp[i] = make([]int, V+1)
    }

    for i := 1; i <= N; i++ {
        for j := 1; j <= V; j++ {
            item := int(j/vw[i-1][0]) + 1
            for k := 0; k < item; k++ {
                if j-k*vw[i-1][0] >= 0 {
                    dp[i][j] = max(max(dp[i-1][j], dp[i-1][j-k*vw[i-1][0]]+k*vw[i-1][1]), dp[i][j])
                }
            }
        }
    }
    return dp[N][V]
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

# a.txt

4 5
1 2
2 4
3 4
4 5

# how to run
go run script.go < a.txt