Codeforces Round #257 (Div. 2), problem: (B) Jzzhu and Sequences solution

Codeforces Round #257 (Div. 2), problem: (B) Jzzhu and Sequences: http://codeforces.com/contest/450/problem/B

Codeforces Round #257 (Div. 2), problem: (B) Jzzhu and Sequences editorial: http://codeforces.com/blog/entry/13112

Codeforces Round #257 (Div. 2), problem: (B) Jzzhu and Sequences solution: http://ideone.com/Eh6hpS

#include <iostream>
#include <cstdio>
using namespace std;

int main() {
    long long int x, y, z, n, tmp, a[7]={0}, ans;
    const int md=1e9+7;
    scanf("%I64d%I64d", &x, &y);
    scanf("%I64d", &n);
    z=y-x, a[1]=x, a[2]=y;
    for(int i=3; i<=6; i++) {
        tmp=x, x=y, y=z, z=y-x, a[i%6]=y;
    }
    if(a[n%6]>=0) printf("%I64d", a[n%6]%md);
    else printf("%I64d", (md+a[n%6]%md)%md);
    return 0;
}

note: to learn about mod operation on negative numbers: http://math.stackexchange.com/questions/519845/modulo-of-a-negative-number