https://www.acmicpc.net/problem/10156
const fs=require('fs')
let input=fs.readFileSync('/dev/stdin').toString().split(' ')
var k=parseInt(input[0])
var n=parseInt(input[1])
var m=parseInt(input[2])
var sum=k*n-m
if(sum>0) console.log(sum)
else console.log(0)