http://codeforces.com/contest/1027/problem/B
#include<bits/stdc++.h>
using namespace std;
int main()
{
long long n,q;
cin>>n>>q;
while(q--)
{
long long x,y;
scanf("%I64d %I64d",&x,&y);
if(n%2==0)
{
long long tmp=(x-1)*(n/2)+(y-1)/2+1;
if((x+y)%2==0)
printf("%I64d
",tmp);
else
printf("%I64d
",n*n/2+tmp);
}
else
{
if((x+y)%2==0)
{
long long tmp=(x-1)/2*n+(y-1)/2+1;
if(x%2==0)
{
printf("%I64d
",tmp+n/2+1);
}
else
{
printf("%I64d
",tmp);
}
}
else
{
long long tmp=(x-1)/2*n+(y-1)/2+1+n*n/2+1;
if(x%2==0)
{
printf("%I64d
",n/2+tmp);
}
else
{
printf("%I64d
",tmp);
}
}
}
}
return 0;
}分多种情况讨论，推公式就行。