C. Letter：题目

#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int> a((int)6e5);
vector<int> b((int)6e5), c[(int)6e5];
const int mod = 1e9 + 7;
string s;
signed main()
{cin>>s;int n = s.length();s = "1"+s+"1";for (int i=1;i<=n;i++){a[i] = a[i-1];if (s[i]<='z'&&s[i]>='a') a[i]++;}for (int i=n;i>=1;i--){b[i] = b[i+1];if (s[i]<='Z'&&s[i]>='A') b[i]++;}int res = 0x3f3f3f3f;for (int i=1;i<=n;i++){res = min(res,a[i-1]+b[i+1]);}cout<<res<<endl;
}