[KOI]전국본선 2014 중등부 두번째 문제

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#include <stdio.h>   int seat[2000][2001];   int gcd(int a, int b) {     return (b) ? gcd(b, a % b) : (a); }   int main() {     int ret = 0;     int from, to;     scanf("%d %d", &from, &to);     for (int i = from; i <= to; ++i) {         for (int j = 0; j < i; ++j) {             int g = gcd(i, j);             int up = j / g;             int down = i / g;             if (seat[up][down] == 0) {                 seat[up][down] = 1;                 ++ret;             }         }     }     printf("%d\n", ret);     return 0; }