#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
#define Inf 1000000001
vector<int> N(1000),K(1000);
int dp[1001][2];
bool f[1001][2];
int get(int turn,int player){
	if(turn==1000)return 0;
	if(f[turn][player])return dp[turn][player];
	f[turn][player] = true;
	int r = N[turn] % (K[turn]+1);
	int ret = -Inf;
	if(r==0){
		ret = max(get(turn+1,player), -get(turn+1,player^1))-1;
	}
	else if(r==1){
		ret = min(get(turn+1,player), -get(turn+1,player^1)) + 1;
	}
	else{
		ret = max(ret, max(get(turn+1,player), -get(turn+1,player^1))-1);
		ret = max(ret, min(get(turn+1,player), -get(turn+1,player^1)) + 1);
	}
	dp[turn][player] = ret;
	return ret;
}
	

int main(){
	rep(i,1000)cin>>N[i]>>K[i];
	
	int ans = get(0,0);
	rep(i,1001){
		if(i-(1000-i)==ans){
			cout<<i<<endl;
			return 0;
		}
	}
	
	return 0;
}