#include <iostream> #include <string> using namespace std; int r[52], g[52]; int min(int a, int b){return a <b?a:b;} int main() { string str; cin >> str; int l = str.length(); r[0] = g[0] = 0; for (int i = 1; i <= l; i++)//弄个前缀和 { r[i] = r[i-1]; g[i] = g[i-1]; if (str[i-1] == 'R')r[i]++; else g[i]++; } int ans = l;//显然最大不会超过l for (int i = 0; i <= l; i++) ans = min(ans, g[i]+r[l]-r[i]);//枚举所有位置试一下 把前面的全部刷成R,后面的刷成G cout << ans; }